Headache on the Left Side: Causes and When to Worry

Headache on the Left Side of the Head — Causes, Patterns and When to Worry

Why a headache can stay on one side, what usually causes it, the patterns worth checking, and the warning signs that need urgent care. Explained by a Sydney neurologist.

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When a Headache on One Side Needs Urgent Care

Most headaches on one side of the head are migraine, which is common and not dangerous. A few patterns need care straight away, so they come first. Everything on this page applies to the right side as well as the left.

Call 000 — or go to an emergency department — if

a headache comes on suddenly and severely and reaches its worst within a minute (the worst headache of your life), even if it then eases
a very high blood pressure reading (a top number of 180 or more, or a bottom number of 120 or more) comes with chest or back pain, shortness of breath, vomiting, problems with your eyesight, confusion or a seizure: call 000 straight away
your blood pressure is still very high when you measure it again after 5 minutes of sitting quietly, and you have a headache
the headache comes with fever and a stiff neck, a rash that does not fade when pressed, confusion or unusual drowsiness
you are over 50 with a new headache, or a change in your usual headaches, and you notice blurring, double vision, or sight that dims or goes dark in one eye, even if it lasts only a few minutes
the headache comes with sudden loss or dimming of vision (even if brief), double vision, a new drooping eyelid or one pupil larger than the other, slurred speech, sudden severe dizziness or unsteadiness, or numbness, weakness or drooping of the face, an arm or a leg
an eye becomes painful and red, with blurred vision, halos (coloured rings) around lights, or nausea and vomiting
the headache started after a head injury and is getting worse, comes with vomiting, drowsiness or confusion, or you take blood-thinning medicine
the headache comes with a seizure
you are more than 20 weeks pregnant or had a baby in the last 6 weeks and have a severe headache, a headache that does not get better with simple pain relief, blurred vision or flashing lights, sudden swelling of the face, hands or feet, pain under the ribs or in the upper tummy, vomiting with a headache, or a reading of 160/110 or more: go to your maternity unit or an emergency department now; call 000 for a seizure, trouble breathing or chest pain
you have a spinal cord injury at mid-chest level or higher and get a sudden, pounding headache, often with sweating or flushing above the injury: sit upright with your legs down, loosen anything tight, check your bladder, catheter and bowel, and follow your own dysreflexia plan if you have one; call 000 if it does not settle within a few minutes or you cannot find the cause

A sudden, explosive headache, wherever it is felt, can mean bleeding around or into the brain (a subarachnoid or intracerebral haemorrhage). A very high reading with chest or back pain or shortness of breath can mean the heart or the main artery from the heart is under strain; with vomiting, problems with eyesight, confusion or a seizure, it can mean the pressure is affecting the brain (hypertensive encephalopathy). A very high reading with a headache needs checking in an emergency department, because only tests can show whether the pressure is harming the brain, heart, eyes or kidneys. In someone over 50, a new headache with a change in vision can mean giant cell arteritis is cutting off the blood supply to the eye (see below): treated the same day, sight can usually be saved, but sight that is lost rarely comes back. Weakness, numbness or drooping of the face, trouble speaking, sudden unsteadiness or a sudden loss of vision can mean a stroke. Double vision, a new drooping eyelid or a change in the size of one pupil can mean pressure on a nerve from a bulging blood vessel (an aneurysm) or a tear in the wall of an artery in the neck (a dissection). A painful red eye with blurred vision and halos can mean a sudden rise in the pressure inside the eye (acute angle-closure glaucoma), which can permanently damage sight if it is not treated quickly. After a head injury, bleeding inside the skull can build up over hours, sometimes after a spell of feeling well. Fever with a stiff neck, or a rash that does not fade when pressed, can mean meningitis. A seizure with a headache needs urgent checks for a cause in the brain. In pregnancy or after a birth, a severe headache can be the first sign of pre-eclampsia, a condition of high blood pressure in pregnancy that can lead to seizures; after a spinal cord injury, a pounding headache can be autonomic dysreflexia, a sudden surge in blood pressure set off by something below the injury, such as a full bladder. In both, lower readings than 180/120 count: in pregnancy, 140/90 is high and 160/110 is severe; after a spinal cord injury, a rise in the top number of 20 to 40 or more above your usual reading matters, and 130/90 can already be high. All need urgent treatment. If you have migraine, your usual aura (shimmering or zigzag lines that spread slowly over several minutes and clear within an hour) does not need 000 on its own, and nor do the eye signs of attacks a doctor has already diagnosed as cluster headache (a red, watering eye, a drooping eyelid or a smaller pupil). A first cluster-like attack, a first aura after 50, or an attack or aura that is different from your usual ones needs an emergency department the same day; call 000 if it comes with a new drooping eyelid, one pupil larger than the other, or a very high reading. In the same way, vomiting in your usual migraine attack does not need 000 on its own; with a very high reading, it does. Remember FAST: Face drooping, Arm weakness, Speech difficulty, Time to call 000.

See your GP the same day if

it is a new headache, or a change in your usual headaches, and you are over 50, especially with a new tender scalp that does not go away, pain in the jaw when you chew that eases when you stop, aching shoulders, or feeling generally unwell; with any change in your vision, see the list above
a new headache on one side, unlike your usual headaches, comes with new pain on the same side of the neck, or with a ringing or whooshing in the ear that started suddenly, especially after a neck injury, a sudden twist or stretch of the neck, or neck manipulation: go to an emergency department the same day; with a new drooping eyelid or one pupil larger than the other, or any other sign in the list above, call 000
a first attack of severe pain in or around one eye or temple, with a red or watering eye or a blocked or runny nostril on that side, or, if you have cluster headache, an attack unlike your usual ones: go to an emergency department the same day; with a new drooping eyelid or one pupil larger than the other, call 000
a rash of small blisters appears on one side of the forehead, temple or scalp, often after 2 or 3 days of burning or tingling pain there; if the rash reaches the tip of the nose, or the eye becomes red, painful or blurred, go to an emergency department the same day
your blood pressure is still very high (a top number of 180 or more, or a bottom number of 120 or more) when you measure it again, even if the headache has gone and you feel well (in pregnancy and after a spinal cord injury, lower readings count: see above)
the headache is getting steadily worse over days or weeks
the headache is worse when you lie down, or is worst on waking and comes with vomiting or blurred vision
the headache is brought on by coughing, sneezing, laughing or straining, or comes with a whooshing sound in the ears in time with your heartbeat (if it started suddenly with a new headache on one side, go to an emergency department the same day: see above)
you have a fever with the headache
it is a new headache, or a change in your usual headaches, and you have, or have had, cancer, or you have a weakened immune system
you are pregnant or have had a baby in the last 6 weeks, or a reading taken from 20 weeks of pregnancy to 6 weeks after the birth is 140/90 or more: contact your midwife, maternity unit or GP the same day; with blurred vision or sudden swelling of the face, hands or feet, contact your maternity unit or go to hospital now

A tear in the wall of an artery in the neck (a dissection) can lead to a stroke in the days after it starts, so it needs a scan of the neck arteries that day. A first attack of severe pain around one eye with a red, watering eye is often cluster headache, but a few conditions that need treatment can look the same, so the first one is checked that day. Shingles near the eye can damage sight, and its treatment works best when it is started early. Fever can mean an infection. Cancer, a weakened immune system, and pregnancy or a recent birth each make some serious causes more likely, so the bar for checking is lower. A very high reading without symptoms is rarely an emergency, but it needs a doctor that day to start or adjust treatment. The other items are explained further down this page. If you cannot see your GP that day, go to an emergency department. If something matches both lists, follow the 000 list.

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These patterns are uncommon. Most headaches on one side of the head are migraine; others come from the neck or the jaw, and a few are cluster headache. None of these damages the brain, and all can be treated. If you are worried about a brain tumour: in a large UK study of family-doctor records, fewer than 1 in 1,000 people who saw their GP with a headache were later found to have one, and tumours usually cause other symptoms too, such as weakness, seizures, confusion, or a headache that gets steadily worse over weeks. These figures do not apply if you have, or have had, cancer, or have a weakened immune system: see your GP the same day about a new headache.

If the Pain Is on the Left, Is Something Wrong on the Left?

It starts behind your left eye, as it did last month and the month before. By lunchtime the whole left side of your head is throbbing, and a search for a headache on the left side offers everything from eye strain to a stroke. It feels logical that pain on the left must mean trouble on the left: in the left eye, the left side of the neck, or the left side of the brain. But if the side of the pain marked the side of a problem, why do so many people with migraine have it on the left in one attack and on the right in the next?

The brain tissue itself cannot feel pain. Pain from the head travels along nerves, and each side of the head has its own: the trigeminal nerve, the main nerve of feeling for the face and head, carries pain from the scalp, the face, the eye, and the coverings and blood vessels of the brain on its own side. In a migraine attack, the pain pathway on one side becomes switched on and oversensitive, so that ordinary signals, even a heartbeat or a step, are felt as pain. Why it is one side in one attack and the other side in the next is not fully understood, but it does not mean that the brain on the painful side is damaged.

There is a second piece of wiring. The nerves from the top of the neck run into the same relay station in the brainstem as the trigeminal nerve, a meeting point doctors call the trigeminocervical complex. In laboratory studies in rats, many of the nerve cells there responded both to the coverings of the brain and to the skin and muscles of the neck, a likely reason that pain can be referred from the neck to the head, and from the head to the neck. So a problem in the upper neck on one side can be felt as a headache over the same side of the head, and a migraine can be felt in the neck. The international classification of headache disorders, the rulebook neurologists use, notes that pain from a nerve at the back of the head can reach the forehead and the eye through these connections. It is a little like two phone lines that ring on the same desk: whoever answers cannot always tell which line the call came in on.

So the side of a headache usually tells you which side's pain pathway is switched on, not where something has gone wrong. For doctors, the more telling question is not which side, but whether the headache ever changes sides. A headache that moves from one side to the other between attacks is typical of migraine. One that is always on the same side, which doctors call side-locked, points to a shorter list of causes, and is worth having checked.

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A headache on one side is felt through the nerves on that side of the head, not in the brain tissue itself. Most one-sided headaches are migraine, and the side, left or right, does not on its own make a headache more serious.

Left or Right: Does the Side Matter?

On its own, rarely. The side of a headache does not point to the heart, to any other organ, or to a particular part of the brain, and none of the headaches in the international classification is defined by being on the left rather than the right. There is no evidence that a headache on the left is more often serious than one on the right: in a study of 477 people with migraine at a Boston headache clinic, whether the pain was on the left or the right made no difference to emergency visits or use of health care. What matters more is the pattern: whether the headache switches sides, how it starts, how long it lasts, and what comes with it.

Migraine is often one-sided, and often switches sides. One-sided pain is one of the four features doctors use to recognise migraine, but a migraine needs only two of them, so it can also be felt on both sides. In a study at a US headache centre of 1,283 people with migraine, two in three had one-sided headaches, the left and the right came up about equally often (24 and 27 in 100), and about another quarter had pain on both sides. Many people find that their migraine is on one side in some attacks and the other side in others. In children and teenagers, migraine is more often on both sides; one-sided pain usually appears in the late teens or early adult life.
Some headaches are side-locked. Cluster headache, and the rarer headaches of the same family described below, are one-sided in every attack, though not always on the same side. In cluster headache the pain usually comes back on the same side throughout a bout, and often for years: in a Nordic study of 383 people with cluster headache, 14 in 100 had ever had attacks switch sides. Hemicrania continua stays on one side in most people: in a London series of 39 people, 36 always had it on the same side. For a headache from the neck, the classification lists side-locked pain among the features that set it apart from migraine and tension-type headache. Trigeminal neuralgia is one-sided by definition. Pain from the jaw, a tooth or a sinus is on the side of the problem when only one side is affected.
Migraine that is always on the same side. In an Italian clinic study of 1,169 people with headaches, 17 in 100 of those with migraine always had their headache on the same side. Most side-locked headaches turn out to be a headache condition in its own right, such as migraine or cluster headache, but a few have another cause on that side, which is why doctors treat side-locking as a reason to look more closely. In an Indian neurology clinic, where 307 people with a headache or face pain that was always on one side all had an MRI scan, 58 in 100 had a headache condition in its own right, migraine most often; 18 in 100 had a headache caused by something else, most often a problem in the neck; and 16 in 100 had a nerve pain of the head or face, such as trigeminal neuralgia. The other causes became more common with age.
Is one side more common? In migraine, studies differ: the left and the right came up about equally often in the US headache centre study, while the Boston clinic found the right more common. Trigeminal neuralgia is a little more often on the right (56 in 100 in a Danish study of 158 people), and so, in some studies, is cluster headache. None of this says anything about how serious a headache is.

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A side-locked headache is not, on its own, a sign of danger: in the Indian clinic study, nearly 6 in 10 turned out to be a headache condition in its own right, such as migraine, and a problem in the neck was the most common of the headaches caused by something else. The check-up is about finding the right diagnosis, because each of these is treated differently.

The Common Causes of a Headache on One Side

Each of these has a typical pattern. No single feature proves one, but together they point to it. The table compares five of them.

Swipe the table sideways to compare all five →

Feature	Migraine	Cluster headache	The neck (cervicogenic headache)	The jaw (TMD)	Hemicrania continua
Where it hurts	Often one side, around the eye, the temple or the forehead; it can affect both sides	Always one side during an attack: in, around or behind one eye, or in the temple	One side, starting in the neck or at the back of the head and spreading forward	The temple and in front of the ear, on one or both sides	One side, all the time
Does it switch sides?	Often, from one attack to the next	Usually the same side for years; in a few people it switches between bouts	Usually not: it stays on the side of the neck problem	Follows the side of the jaw problem	Rarely: about 9 in 10 always have it on the same side
Feels like	Throbbing; moderate to severe; worse with routine activity	Very severe; often described as a hot poker in or behind the eye	An ache that neck movement, or pressing on the neck, can bring on	An ache that is worse when you use the jaw	A constant ache, with flare-ups of moderate or severe pain
How long	4 to 72 hours	15 minutes to 3 hours, from once every other day to 8 times a day, in bouts lasting weeks or months	Comes and goes with neck movement and posture	Comes and goes with jaw use; can last for months	There all the time, for more than 3 months
Other symptoms	Nausea or vomiting, or a dislike of light and noise; sometimes an aura	On the same side: a red, watering eye, a blocked or runny nostril, a drooping eyelid or a smaller pupil; restlessness, pacing	Reduced neck movement	Clicking or grating of the jaw, a stiff jaw	In flare-ups, on the same side: a red, watering eye, a blocked or runny nostril, a drooping eyelid; restlessness

Migraine. By far the most common cause of a headache on one side: about 1 in 7 people worldwide have migraine, against about 1 in 1,000 with cluster headache. It is often felt around the eye, at the temple or across the forehead. It is usually throbbing, moderate to severe and worse with activity, lasts 4 to 72 hours, and comes with nausea or a dislike of light and noise. Stress, missed meals, poor sleep and hormonal changes are among its common triggers. Some people see flashing lights or zigzag lines before the headache: see migraine aura, and our migraine overview.
Cluster headache. Much less common than migraine, and very severe: pain in, around or behind one eye or in the temple, always on one side and usually on the same side throughout a bout, in bouts that last weeks or months. On the same side the eye usually turns red and waters, the nostril blocks or runs, and the eyelid can droop or swell. It affects about 1 in 1,000 people, is three times more common in men, and usually starts between 20 and 40. During a bout, alcohol can set off an attack. It is often missed at first: in a Dutch survey of 1,163 people with cluster headache, a third had seen a dentist and a third an ear, nose and throat specialist before the diagnosis was made. The eye signs settle after each attack. A first attack like this, or one that is different from your usual attacks, needs an emergency department the same day, and 000 if it comes with a new drooping eyelid or one pupil larger than the other. Read more about cluster headache.
The neck (cervicogenic headache). A headache that starts in the neck or at the back of the head and spreads forward over one side, usually the same side, brought on by neck movement, a held posture or pressing on the neck, often with a stiff neck. It comes from a problem in the bones, discs or soft tissues of the neck. See cervicogenic headache.
The jaw (temporomandibular disorder, or TMD). Problems with the jaw joint and the chewing muscles are common, and after toothache they are the most common cause of pain in the face. The pain is usually in the temple and in front of the ear, on one or both sides, and is worse when you chew, talk a lot, yawn, or clench or grind your teeth. The jaw may click, pop or grate, feel stiff, or not open fully. See headache in the temples.
An irritated nerve at the back of the head (occipital neuralgia). Shooting or stabbing pains in the back of the scalp, on one or both sides, lasting from a few seconds to minutes, often with tenderness where the nerve crosses the back of the head and a tingling or sore scalp; the pain can reach the forehead and the eye. A new pain like this needs your GP, because pain from the joints of the upper neck can feel much the same. See headache at the back of the head.
Electric shocks in the face (trigeminal neuralgia). Brief, severe, electric-shock pains on one side of the face, lasting from a fraction of a second to 2 minutes, set off by something as light as a touch, talking, chewing or brushing the teeth. It is felt in the face rather than the head, and a new pain like this needs your GP. See trigeminal neuralgia.
Sinusitis. A blocked nose with thick, discoloured mucus, usually after a cold, with pain or pressure over the cheek or forehead that is worse when the sinus is pressed; when only one side is infected, the pain is on that side. Migraine is often mistaken for sinus headache, partly because it can also block or run the nose; thick, discoloured mucus points to sinusitis. See sinus headache.
Brief stabs (primary stabbing headache, or ice pick headache). Stabs of pain lasting a few seconds, from one to many times a day. They usually move about: in only a third of people do they stay in one fixed place, and they can jump from one side of the head to the other. They are more common in people with migraine, often where the migraine usually hurts. When stabs always strike exactly the same spot, doctors look for a cause at that spot, so a first stab, or stabs always in the same place, should be checked by your GP. See ice pick headache.
A tooth problem. An infected tooth or gum, or an inflamed gum around a partly grown lower wisdom tooth, usually causes toothache or pain in the face, but can spread pain to the head on the same side. Pressing or tapping on the tooth usually makes it worse. See a dentist; with a swollen face or a fever, go the same day.
Shingles. Burning or tingling pain on one side of the forehead, temple or scalp, followed after 2 or 3 days by a rash of small blisters there. Treatment works best when it is started early, so see your GP the same day. If the rash reaches the tip of the nose, or the eye becomes red, painful or blurred, go to an emergency department the same day, because shingles can affect the eye.

A headache on both sides, pressing or tightening like a band, is more often a tension-type headache, the most common headache of all, which is usually felt on both sides. Pain relief taken on too many days a month can itself keep headaches going wherever they are felt: see medication overuse headache.

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The table is a guide, not a diagnosis. Migraine is by far the most common of these, cluster headache affects about 1 in 1,000 people, and many people have more than one kind of headache. Sorting out which headache, or headaches, you have is the main job of a consultation, and each has its own treatment.

The Rarer One-Sided Headaches a Neurologist Looks For

Cluster headache belongs to a small family of headaches that are one-sided in every attack and come with eye or nose signs on that side; doctors call them trigeminal autonomic cephalalgias. The others in the family are rare, but worth knowing about, because each has its own treatment and ordinary headache treatments often do not help.

Paroxysmal hemicrania. Attacks like cluster headache, in and around one eye or temple and with the same eye and nose signs on that side, but shorter and more frequent: 2 to 30 minutes, more than 5 times a day. Unlike cluster headache, it is not more common in men. It responds completely to one particular medicine, which is part of how it is confirmed.
SUNCT and SUNA. Attacks of stabbing pain around one eye or temple, lasting from 1 second to 10 minutes, at least once a day and often many times, usually with a red, watering eye on the same side. Touching the face can set them off, as in trigeminal neuralgia; unlike trigeminal neuralgia, they can usually be set off again straight away.
Hemicrania continua. A headache that is there all the time on one side for more than 3 months, with flare-ups of moderate or severe pain and, on the same side, a red, watering eye, a blocked or runny nostril or a drooping eyelid, or restlessness. Light and noise often bother people during flare-ups, so it can be mistaken for migraine. It responds completely to one particular medicine, which is how a neurologist confirms it.

Because a few conditions in the brain can cause attacks that look like these (for SUNCT, the classification names a problem at the back of the brain as the most common mimic), a neurologist will often arrange an MRI scan.

Where most people sit

These headaches are rare, and they do not damage the brain. They are worth recognising because each has a treatment that usually works, and a neurologist can usually confirm the diagnosis from the pattern of the attacks and how they respond to it.

When a Headache on One Side Has a Serious Cause

A search for a one-sided headache often turns up the frightening possibilities first. They are rare, and nearly all come with a clue that sets them apart.

Giant cell arteritis. After 50, a new headache with a tender scalp (the scalp is often tender during a migraine attack too; in giant cell arteritis the tenderness is new and does not go away), pain in the jaw muscles when you chew, aching shoulders or feeling generally unwell can be giant cell arteritis, an inflammation of the arteries of the head. The headache is often at one or both temples. It needs your GP the same day for blood tests, because it can affect the eyesight: if your sight blurs, doubles or dims, go to an emergency department now. See headache in the temples.
A tear in an artery of the neck (carotid or vertebral artery dissection). A tear in the inner wall of one of the arteries that run up the neck to the brain. It is uncommon: about 3 to 5 in 100,000 people a year in US population studies, and more are being found as scans improve; on average people are in their 40s or around 50 when it is found. It can follow a minor neck injury, a sudden twist or stretch of the neck, or neck manipulation, or happen with no clear cause. Head or neck pain is its most common symptom (80 in 100 in one of those studies), usually on the same side as the tear and often lasting days, and it can be the first or only sign; it can look like migraine or cluster headache. A drooping eyelid and a smaller pupil on the same side (about 1 in 4 in the same study), or a whooshing or ringing sound in the ear that starts suddenly, point strongly to it. It matters because a stroke can follow, sometimes hours or days later. A new headache on one side, unlike your usual headaches, with new pain on the same side of the neck, or with a ringing or whooshing in the ear that started suddenly, needs an emergency department the same day, especially after a neck injury, a sudden twist or stretch of the neck, or neck manipulation; with a new drooping eyelid or one pupil larger than the other, or any sign of a stroke, call 000.
Acute angle-closure glaucoma. A sudden rise in the pressure inside one eye: pain in and around the eye, usually on one side, with a red eye, blurred vision, halos (coloured rings) around lights, and often nausea and vomiting. It is easily mistaken for a headache: in a London series of 38 people, the doctor who first saw them recognised it in only 4 in 10, and a wrong diagnosis delayed treatment by almost 6 days on average. It can permanently damage sight, so a painful, red eye with blurred vision or halos around lights needs 000 or an emergency department straight away.
A stroke. A stroke usually causes sudden weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, sudden unsteadiness or a loss of vision, with or without a headache. Call 000 for these signs, whichever side the headache is on, and for a headache that comes on suddenly and severely and reaches its worst within a minute, which can mean bleeding around the brain.
A brain tumour. The worry many people have. Brain tumours are rare: in a large UK study of family-doctor records, fewer than 1 in 1,000 people who saw their GP with a headache were later found to have one. A tumour's headache is not necessarily on the same side as the tumour, so the side of a headache does not point to one. What gives a tumour away is usually something else: the headache is the only symptom in between 2 and 16 in 100 people with a brain tumour, and a headache that keeps getting worse is one of its key features (see the lists at the top). If you have, or have had, cancer, or have a weakened immune system, see your GP the same day about a new headache.
Raised pressure inside the head. A headache that is worse lying down or first thing in the morning, sometimes with vomiting or blurred vision, and that gets steadily worse, can mean pressure is building up inside the head, for example from a blockage of the fluid pathways or, rarely, a tumour. Raised pressure of the fluid around the brain without a tumour (idiopathic intracranial hypertension) can also cause a whooshing sound in the ears in time with the heartbeat, and is most common in women of child-bearing age. All need your GP the same day, because some can affect sight.

Where most people sit

These causes are rare, and nearly all come with a clue: a sudden explosive start, a change in vision or a painful red eye, weakness or numbness, a new headache after 50, a headache that keeps getting worse, or one that began with a neck injury. A one-sided headache that has come and gone in the same way for years, with a normal examination, is very rarely any of them.

How Is the Cause of a One-Sided Headache Found?

Mostly from your story and an examination. Tests are for when the pattern raises a question.

Your story. Which side, and whether it has ever been on the other side; how long attacks last; what comes with them, such as a watering eye, a blocked nostril or a drooping eyelid; what brings them on; how often you take pain relief; and anything new, such as a neck injury, a rash or a change in your vision.
The examination. A full neurological examination, including the eyes, the pupils and eyelids, the back of the eyes, and your blood pressure, and a check of the neck, the jaw, the scalp and the arteries at the temples.
A headache diary. Note the side each time. A few weeks of a headache diary shows whether your headache switches sides, how long the attacks last, and what sets them off.
A scan, when it will change what happens next. When the pattern fits migraine and the examination is normal, a scan is not needed. The Australian and New Zealand Association of Neurologists advises against brain scans for long-standing headaches like migraine: in people with recurring migraine or tension-type headaches and a normal examination, a CT or MRI scan finds a significant problem in fewer than 1 in 100, and in some studies as few as 2 in 1,000. A scan is arranged when the pattern points away from the common causes: a headache that has always been on the same side, one-sided attacks with a red, watering eye or a drooping eyelid, a headache that has changed, or a warning sign in the lists at the top. When a tear in an artery of the neck is possible, the arteries themselves are scanned, because an ordinary brain scan can miss it.
Blood tests, an eye check or a dental check, when they fit. Blood tests for inflammation when a new headache starts after 50 (an ordinary brain scan is not the test for giant cell arteritis, so a normal brain scan does not rule it out); an eye check of the pressure inside the eye; a dental check of the teeth and the jaw joint.

What Helps a Headache on One Side

The treatment depends on the cause, which is why the diagnosis comes first. These help most people.

For a migraine today. Rest in a dark, quiet room, and take simple pain relief early in the attack, at the dose on the pack. Ask your pharmacist which kind suits you, especially if you are pregnant, have other health conditions or take other medicines. If simple pain relief is not enough, your doctor can prescribe a migraine medicine.
Keep pain relief to two or three days a week at most, and to fewer than 10 days a month for some kinds. Taking it on too many days (15 or more days a month for simple pain relievers, 10 or more for some others) can itself keep headaches going; ask your pharmacist which yours is, and see medication overuse headache.
Cluster headache has its own treatments, both for the attacks and to prevent them during a bout, so it needs a doctor's diagnosis. See cluster headache.
The neck. Physiotherapy, with exercises for the neck and shoulders and hands-on treatment, is the usual first step for a headache from the neck: see cervicogenic headache.
The jaw. Rest it with softer food for a while, no chewing gum and no very wide yawns, and notice when you clench so you can let the jaw relax. For jaw pain that has lasted 3 months or more, an international guideline recommends jaw exercises and stretching, hands-on therapy and posture exercises guided by a physiotherapist, and psychological therapy for pain, such as cognitive behavioural therapy.
The rarer one-sided headaches each have their own treatment, which a neurologist can advise on.
Prevention, when headaches are frequent. A headache diary, regular sleep and meals, enough water, regular exercise and ways to manage stress reduce how often many headaches come. Preventive medicines can reduce how often migraine and cluster attacks come; your doctor can advise whether one suits you.

When to See a Neurologist About a Headache on One Side

A headache that is always on the same side and has never switched
One-sided attacks with a red, watering eye, a blocked or runny nostril or a drooping eyelid
A constant headache on one side that never fully goes away
Headaches on many days a month, or pain relief needed on more than two or three days a week
You are not sure whether it is migraine, your neck, your jaw or something else
A headache that has changed, or a new kind of headache (see your GP first; a new headache after 50 needs your GP the same day)
You want a clear diagnosis and a plan

A consultation involves a detailed history, a neurological examination and a plan: working out which headache, or headaches, you have, arranging tests when the result will change what happens next, and coordinating with your GP and, when needed, a physiotherapist, a dentist or an eye specialist. Dr Ron Granot trained at Prince of Wales Hospital, Sydney, and sees patients in Bondi Junction. For the wider picture, read our migraine overview.

Frequently Asked Questions

What does it mean if my headache is on the left side? +

Usually nothing about the left side in particular: the side of a headache does not point to the heart, to any other organ, or to a particular part of the brain. A headache on one side is most often migraine, which can be on the left in one attack and on the right in the next; stress, poor sleep and missed meals are common triggers. Other common causes are a problem in the neck or the jaw on that side, and cluster headache, which causes very severe pain around one eye. What matters more than the side is the pattern, and a headache that is always on the same side is worth showing your GP. Call 000 for a headache that comes on suddenly and severely, reaching its worst within a minute, or comes with fever and a stiff neck, confusion, weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision, a painful red eye with blurred vision or halos around lights, or a seizure.

When should I worry about a headache on the left side of my head? +

Call 000 or go to an emergency department if it comes on suddenly and severely, reaching its worst within a minute, even if it then eases; if it comes with fever and a stiff neck, a rash that does not fade when pressed, confusion, weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, sudden unsteadiness, a loss of vision, double vision, a new drooping eyelid or one pupil larger than the other, or a seizure; if an eye becomes painful and red, with blurred vision or halos around lights; if you are over 50 with a new headache, or a change in your usual headaches, and notice blurring, double vision or sight that dims or goes dark in one eye; if you have a very high blood pressure reading with the headache (see the list at the top; in pregnancy and after a spinal cord injury, lower readings count); or if it started after a head injury and is getting worse, comes with vomiting, drowsiness or confusion, or you take blood-thinning medicine. Your usual migraine aura, or the eye signs of attacks a doctor has already diagnosed as cluster headache, do not need 000 on their own; a first cluster-like attack, a first aura after 50, or an attack or aura unlike your usual ones needs an emergency department the same day, and 000 if it comes with a new drooping eyelid or one pupil larger than the other. Go to an emergency department the same day, too, for a new headache on one side, unlike your usual headaches, with new pain on the same side of the neck, or with a ringing or whooshing in the ear that started suddenly, especially after a neck injury, a sudden twist or stretch of the neck, or neck manipulation; or for a rash of blisters on one side of the forehead that reaches the tip of the nose or makes the eye red, painful or blurred. See your GP the same day if it is new after 50, is getting steadily worse, is worse when you lie down, or is worst on waking with vomiting or blurred vision, is brought on by coughing or straining, comes with a fever or a blistering rash, or is a new headache and you have, or have had, cancer, or have a weakened immune system. If you are more than 20 weeks pregnant or had a baby in the last 6 weeks, a severe headache, or one that does not get better with simple pain relief, needs your maternity unit or an emergency department now; any other headache in pregnancy or in the 6 weeks after a birth needs your midwife, maternity unit or GP the same day.

Is a headache on the left side a sign of a stroke? +

Rarely on its own. A stroke usually causes sudden weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, sudden unsteadiness or a loss of vision, with or without a headache. Call 000 straight away for any of these, whichever side the headache is on, even if they go away: remember FAST, Face drooping, Arm weakness, Speech difficulty, Time to call 000. Call 000 too for a headache that comes on suddenly and severely and reaches its worst within a minute, even if it then eases, because it can mean bleeding around the brain. A new headache on one side, unlike your usual headaches, with new pain on the same side of the neck, or with a ringing or whooshing in the ear that started suddenly, can come from a tear in an artery of the neck, which can lead to a stroke, especially after a neck injury, a sudden twist or stretch of the neck, or neck manipulation: go to an emergency department the same day, or call 000 with a new drooping eyelid, one pupil larger than the other, or any sign of a stroke. If you have migraine, your usual aura (shimmering or zigzag lines that spread slowly over several minutes and clear within an hour) does not need 000 on its own; a first aura after 50, or one that is different from your usual aura, needs an emergency department the same day.

Could a headache on one side be a brain tumour? +

Very rarely. In a large UK study of family-doctor records, fewer than 1 in 1,000 people who saw their GP with a headache were later found to have a brain tumour, and a tumour's headache is not necessarily on the same side as the tumour, so the side does not point to one. Tumours usually cause other problems too: the headache is the only symptom in between 2 and 16 in 100 people with a brain tumour. Call 000 for weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or a seizure. See your GP the same day for a headache that gets steadily worse over days or weeks, is worse when you lie down, or is worst on waking with vomiting or blurred vision. A headache that has always been on the same side is worth an examination by your GP, and sometimes a scan, even though most turn out to be migraine or another headache condition in its own right. These figures do not apply if you have, or have had, cancer, or have a weakened immune system: see your GP the same day about a new headache.

Why is my headache always on the same side? +

Some headaches stay on one side by nature. Cluster headache usually comes back on the same side, often for years; a headache from the neck usually stays on the side of the neck problem; hemicrania continua, a rare headache that is there all the time, stays on one side in most people; and in some people with migraine (about 1 in 6 in one clinic study), it always comes on the same side. In one clinic study, nearly 6 in 10 side-locked headaches turned out to be a headache condition in its own right, such as migraine or cluster headache, but because a few have another cause on that side, a headache that has always been on one side is worth an examination by your GP or a neurologist, and sometimes a scan. See your GP the same day if it is a new headache and you are over 50, is getting steadily worse, or is worse when you lie down. Call 000 if it comes with weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision, or a new drooping eyelid or one pupil larger than the other; the eye signs of attacks a doctor has already diagnosed as cluster headache do not need 000 on their own, but a first attack, or one that is different, needs an emergency department the same day, and 000 if it comes with a new drooping eyelid or one pupil larger than the other.

Can a headache on one side come from the neck? +

Yes. The nerves of the upper neck feed into the same relay station in the brainstem as the main nerve of feeling for the head, so a problem in the bones, discs or soft tissues of the neck can be felt as a headache over the same side of the head (cervicogenic headache). It usually starts in the neck or at the back of the head, spreads forward, usually stays on the same side, and is brought on by neck movement, a held posture or pressing on the neck. Shooting pains up the back of the head on one side can come from an irritated nerve there (occipital neuralgia); a new pain like this needs your GP. Rarely, a new headache on one side, unlike your usual headaches, with new pain on the same side of the neck, or with a ringing or whooshing in the ear that started suddenly, comes from a tear in an artery of the neck, especially after a neck injury, a sudden twist or stretch of the neck, or neck manipulation: go to an emergency department the same day, or call 000 with a new drooping eyelid, one pupil larger than the other, weakness, numbness, trouble speaking or a loss of vision.

Why does my eye hurt with a headache on one side? +

Migraine often hurts around or behind one eye: in a large study at a US headache centre, about 2 in 3 people with migraine felt pain around the eyes. Cluster headache causes very severe pain in, around or behind one eye, with a red, watering eye, a blocked or runny nostril or a drooping eyelid on that side, in attacks of 15 minutes to 3 hours. Less often the cause is the eye itself, shingles, or, after 50, an inflamed artery (giant cell arteritis), which needs your GP the same day, especially with a new tender scalp that does not go away or pain in the jaw when you chew. Call 000 or go to an emergency department now for a painful, red eye with blurred vision or halos around lights; for sudden loss of vision, double vision, a new drooping eyelid or one pupil larger than the other; or, if you are over 50, for blurring, double vision or dimming of sight with a new headache, or a change in your usual headaches. The eye signs of attacks a doctor has already diagnosed as cluster headache do not need 000 on their own; a first attack, or one that is different, needs an emergency department the same day, and 000 if it comes with a new drooping eyelid or one pupil larger than the other. A rash of blisters on one side of the forehead or scalp needs your GP the same day, and an emergency department the same day if it reaches the tip of the nose or makes the eye red, painful or blurred.

How do I get rid of a headache on the left side? +

It depends on the cause. For a migraine, rest in a dark, quiet room and take simple pain relief early, at the dose on the pack (if you are pregnant, ask your pharmacist which kind is safe); if that is not enough, your doctor can prescribe a migraine medicine. For a headache from the neck, physiotherapy is the usual first step; for the jaw, rest it with softer food, avoid chewing gum and try not to clench. Cluster headache has its own treatments, so it needs a doctor's diagnosis. Keep pain relief to two or three days a week at most, and to fewer than 10 days a month for some kinds (your pharmacist can tell you which), because taking it more often can itself keep headaches going. If you are more than 20 weeks pregnant or had a baby in the last 6 weeks, a severe headache, or one that does not get better with simple pain relief, needs your maternity unit or an emergency department now; any other headache in pregnancy or in the 6 weeks after a birth needs your midwife, maternity unit or GP the same day. Call 000 for a headache that comes on suddenly and severely, reaching its worst within a minute, or comes with fever and a stiff neck, confusion, weakness, numbness or drooping of the face, an arm or a leg, trouble speaking, a loss of vision or a seizure.

Important: This page is general health information for adults living in Australia and is not a substitute for individual medical advice. If you have a sudden, severe headache that reaches its worst within a minute, a very high blood pressure reading (a top number of 180 or more, or a bottom number of 120 or more) with a headache, a headache with a stiff neck and fever, confusion, a headache with weakness, numbness or drooping of the face, an arm or a leg, sudden loss of vision, double vision, slurred speech or sudden unsteadiness, a painful red eye with blurred vision, a headache that is getting worse after a head injury, a seizure, or, if you are over 50, a new headache with blurring, double vision or dimming of sight, or any other warning sign listed at the top of this page, call 000 or go to an emergency department. If you are more than 20 weeks pregnant or had a baby in the last 6 weeks and have a severe headache, blurred vision or flashing lights, go to your maternity unit or an emergency department now. Diagnosis and treatment decisions are made on an individual basis with your treating doctor.

Sources: the studies and guidelines behind this page

The international classification of headache disorders (sections 1.1, 1.2, 2.1, 3, 3.1, 3.2, 3.3, 3.4, 4.7, 6.4.1, 6.5.1, 7.4.1, 11.2.1, 11.3.1, 11.5.1, 11.6, 11.7, 13.1.1, 13.1.2.1 and 13.4): Headache Classification Committee of the International Headache Society. Cephalalgia 2018;38:1-211. PubMed 29368949
How common migraine and cluster headache are: Stovner LJ, et al. J Headache Pain 2022;23:34 (PubMed 35410119); Fischera M, et al. Cephalalgia 2008;28:614-8 (PubMed 18422717).
Where migraine hurts, and left against right: Kelman L. Headache 2005;45:1038-47 (the US headache centre study of 1,283 people; PubMed 16109118); Loder E, et al. Pain Res Manag 2018;2018:6157982 (the Boston study of 477 people; PubMed 29973968).
Side-locked headache: Leone M, et al. Headache 1993;33:381-4 (the Italian study of 1,169 people; PubMed 8376099); Prakash S, et al. Headache 2016;56:1183-93 (the Indian clinic study of 307 people; PubMed 27256162); Prakash S, Rathore C. J Headache Pain 2016;17:95 (PubMed 27770404).
Which side, and switching sides: Meyer EL, et al. J Headache Pain 2009;10:259-63 (the Nordic study of 383 people with cluster headache; PubMed 19495933); Cho S, et al. J Clin Neurol 2025;21:220-9 (PubMed 40308017); Maarbjerg S, et al. Headache 2014;54:1574-82 (the Danish study of 158 people with trigeminal neuralgia; PubMed 25231219); Cittadini E, Goadsby PJ. Brain 2010;133:1973-86 (the London series of 39 people with hemicrania continua; PubMed 20558416).
Cluster headache before diagnosis (the Dutch survey of 1,163 people): van Vliet JA, et al. J Neurol Neurosurg Psychiatry 2003;74:1123-5. PubMed 12876249
The neck and the head (laboratory studies): Bartsch T, Goadsby PJ. Brain 2002;125:1496-509 (PubMed 12077000) and Brain 2003;126:1801-13 (PubMed 12821523).
A tear in an artery of the neck: Lee VH, et al. Neurology 2006;67:1809-12 (the US population study; PubMed 17130413); Silbert PL, et al. Neurology 1995;45:1517-22 (PubMed 7644051); Griffin KJ, et al. Stroke 2024;55:670-7 (PubMed 38288608); Arning C, et al. Dtsch Arztebl Int 2022;119:581-7 (PubMed 35734920); Engelter ST, et al. Neurology 2013;80:1950-7 (PubMed 23635964).
Acute angle-closure glaucoma (the London series of 38 people): Siriwardena D, et al. Age Ageing 1996;25:421-3. PubMed 9003875
Brain tumours (the UK study of family-doctor records): Hamilton W, Kernick D. Br J Gen Pract 2007;57:695-9. PubMed 17761056
Jaw pain lasting 3 months or more (the international guideline): Busse JW, et al. BMJ 2023;383:e076227. PubMed 38101929
Guidance: Australian and New Zealand Association of Neurologists, Choosing Wisely Australia recommendation on brain imaging for non-acute primary headache; healthdirect, Cluster headache, Glaucoma, Shingles and Stroke; Stroke Foundation, Signs of stroke; Headache Australia, Hemicrania continua; NHS, Cluster headaches and Temporal arteritis.

A Headache on One Side?

Book a consultation with Dr Ron Granot — neurologist with a special interest in headache, Bondi Junction. Ask your GP for a referral, then get in touch.

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Call Us02 9388 0615

LocationSuite 301, Bondi Junction

Emailreception@eastneurology.com.au

Last reviewed: 17 October 2026 by Dr Ron Granot, FRACP — Consultant Neurologist, East Neurology, Bondi Junction.