What is a cluster headache?

Short answer

A cluster headache is a specific, rare headache disorder — not a bad migraine. Attacks are strictly on one side, centred around or behind one eye, extremely severe, and short: 15 minutes to 3 hours. That eye goes red and waters, the nostril on the same side blocks or runs, and the eyelid may droop. They come in "clusters" — daily bouts for weeks, often at the same hour, frequently waking people at night — then vanish for months. It affects about 1 in 1,000 people, roughly three times more men than women, and it is routinely misdiagnosed as migraine, sinus or dental trouble for years.

Cluster headache needs a doctor to diagnose, not a survey — but if some of your attacks might be migraine, Welltory's 2-minute check-in shows the stress-and-recovery pattern in your nervous system behind them.

Note: this article explains what cluster headache is and is not medical advice. It is a distinct condition that needs specialist diagnosis and specific treatment — if the pattern below fits, see a doctor and name it.

If this is you, you are probably not being taken seriously enough

Cluster headache has a grim nickname — "suicide headache" — because the pain is rated among the most severe a human can experience, worse than childbirth or a fracture by many patients' accounts. And yet it is one of the most misdiagnosed conditions in medicine. In one hospital series, about three-quarters of people were given the wrong diagnosis at their first consultation — usually migraine, sinusitis or a dental problem — and many waited years for the right name.

So if you have been told it is "just migraines" or "your sinuses" and nothing has worked, and the attacks match what is below, you are not imagining it and you are not overreacting. This is a distinct condition with its own specific treatments, and getting the label right is what unlocks them. It is not your fault that it was missed — it is genuinely hard to recognise if you have not seen it before, which most non-specialists have not.

What an attack actually looks like

The picture is unusually consistent, which is what makes it recognisable once you know it. Drawing on the formal diagnostic criteria:

The pain. Severe to very severe, strictly on one side, centred in, around or behind one eye or the temple. It builds fast — minutes — to an intensity people describe as a hot poker or a drill behind the eye.

How long. Short, by headache standards: 15 minutes to 3 hours untreated. This alone separates it from migraine, which runs 4 to 72 hours.

The eye and nose, same side as the pain. A red, watering eye; a blocked or running nostril; a drooping or swollen eyelid; sometimes sweating on that side of the forehead, or a smaller pupil. These "autonomic" signs are on the same side as the pain, and they are a hallmark — migraine does not do this in the same clear, one-sided way.

Restlessness. This is the tell that surprises people. During a cluster attack, most people cannot keep still — they pace, rock, press on the eye. That is the opposite of migraine, where people lie down in the dark and stay motionless because movement makes it worse.

Frequency. From one attack every other day up to eight a day during a bout.

Why it is called a "cluster"

The name is about timing, and the timing is the second big clue.

Attacks come in bouts — a cluster period — lasting weeks to a couple of months, during which they strike daily or near-daily. Then the condition goes into remission for months or even years before the next bout. Many people get a bout at the same time of year, often spring or autumn.

Within a bout, the attacks are strikingly punctual. A large analysis found a clear daily rhythm in about 70% of people, with a peak in the small hours of the morning — which is why cluster headache so often wakes people from sleep at the same time each night. This clockwork quality points to the brain's internal timekeeper, the hypothalamus, which imaging shows is active during attacks. It is one of the few headaches genuinely tied to the body clock.

Why it gets mistaken for other things for so long

Understanding the misdiagnosis is worth a moment, because it is how you avoid adding years to your own.

Mistaken for migraine. This is the commonest error, and it is understandable — both are severe one-sided headaches. But the giveaways are there if you look: cluster attacks are far shorter, the person is restless rather than still, and the red watering eye and blocked nostril on one side are not migraine's usual signature. The cost of this mix-up is specific — a migraine diagnosis never comes with the oxygen or injectable treatment that actually aborts a cluster attack.

Mistaken for sinusitis. The pain sits around the eye and the nose runs, so "sinus infection" is an easy call — except there is no infection, antibiotics and decongestants do nothing, and the attacks come and go on a clockwork schedule no sinus problem follows.

Mistaken for a dental problem. Because the pain can radiate into the upper teeth and jaw on one side, some people have dental work — even extractions — before the real cause is found. If tooth pain comes in one-sided attacks with a watering eye and then vanishes for months, teeth are not the issue.

The through-line is that cluster headache is rhythmic and comes with one-sided eye and nose signs, and none of the conditions it gets confused with behave that way. Knowing that is often what finally ends the wrong-turn cycle.

Cluster or migraine? The differences that matter

People get sent down the migraine path for years, so this is worth laying out plainly.

If several of the left-column features fit — especially the short attacks, the restlessness, and the red watering eye on one side — that is worth raising as cluster headache specifically, by name, with a doctor.

Why it skews male, and what that is not

Cluster headache is one of the few headache disorders more common in men — the classification puts it at about three times more often than women, and it typically starts between 20 and 40. That is simply the epidemiology; it does not mean a woman cannot have it (many do and are missed for even longer, precisely because it is thought of as a "man's" headache), and it does not mean it is caused by anything to do with masculinity or testosterone. The male skew is real and unexplained, and its main practical use is as one more clue on the list, not a rule.

Episodic and chronic: how the condition runs over time

There are two courses it takes, and knowing which one you have shapes the plan.

Episodic is the common form: bouts lasting weeks to a couple of months, separated by remission periods of at least three months — often much longer — when you are completely free of attacks. Many people can almost set a calendar by it, with a bout arriving at the same season each year.

Chronic is the harder form: attacks continue for more than a year with no remission, or with gaps shorter than three months. It is less common, and it is the situation where specialist care matters most, because the usual "get through the bout and then you're clear" approach does not apply.

Either way, the shape over time is part of the diagnosis. A headache that genuinely disappears for months and then returns in a concentrated run is behaving like cluster headache and unlike almost anything it gets confused with — migraine does not switch cleanly on and off by the calendar, and neither do sinus or dental problems. When you track the start and end of a bout, you are not just managing it; you are giving a doctor one of the most recognisable features there is.

Triggers during a bout

Outside a cluster period, the usual triggers do nothing. Inside one, they are potent — and the standout is alcohol. During a bout, even a small drink can set off a full attack, often within an hour. Nitroglycerin (a heart medication) and strong smells can do the same. The practical takeaway most specialists give: avoid alcohol entirely for the duration of a bout. Between bouts it does not have this effect, which is itself a diagnostic clue.

What actually treats it — and what does not

This is the part that makes diagnosis worth chasing, because the effective treatments are specific and unusual.

What does not work: ordinary painkillers. An attack peaks and fades within an hour or so, faster than a swallowed tablet can act, so paracetamol or ibuprofen are essentially useless here. Reaching for them repeatedly is one reason people conclude "nothing helps."

What does work, according to the American Migraine Foundation and headache specialists: breathing high-flow oxygen through a mask at the start of an attack, and fast-acting triptans given by injection or nasal spray (not tablets, which are too slow). These abort attacks in minutes for many people. There are also preventive treatments taken through a bout to cut attacks down.

The reason this matters so much: someone told they have migraine will never be offered oxygen, because oxygen does nothing for migraine. The treatment only appears once the diagnosis is right.

What your own data can add

A wearable cannot diagnose cluster headache — the red watering eye and the one-sided pattern are what a doctor uses. But it can capture the one feature that is uniquely measurable here: the clock.

What to look at. Because cluster attacks so often strike at the same time of night, your sleep and overnight heart-rate data can show the pattern plainly — attacks clustering in a particular window, night after night, waking you at a consistent hour. Logging the exact time of each attack against your sleep record turns "they come at night" into "they hit at 2–3 a.m. for the last eleven nights", which is strong, specific evidence of the rhythm that defines this condition.

Welltory measures heart rate and sleep from your phone or wearable, so the timing of night-time attacks becomes a record rather than a rough memory.

What it cannot do. It cannot see the autonomic signs, cannot tell cluster from migraine, and cannot replace a specialist. What it does is document the rhythmicity — and rhythmicity is exactly the thing that distinguishes cluster headache and that people struggle to convey in words at an appointment.

Not sure if it is cluster or migraine?

For the migraine side of the picture, Welltory's 2-minute check-in shows the stress-and-recovery buildup behind attacks. It does not assess cluster headache — that is a conversation with a specialist — but if migraine is also in play, it makes that pattern visible.

When to seek help — and when it is urgent

Cluster headache itself is not dangerous to life, but it is a medical emergency for your quality of life and deserves prompt specialist referral. See a doctor without delay if the attacks match the picture above, and treat these as urgent, because a first severe one-sided headache can occasionally be something else:

• A headache that reaches maximum intensity within seconds — a "thunderclap" — needs emergency care, not a cluster-headache assumption.

• A first-ever severe one-sided headache, especially with any weakness, numbness, confusion or speech or vision changes.

• A drooping eyelid or small pupil that does not go away between attacks (the cluster pattern comes and goes with the attack).

• Fever, or a headache after a head injury.

How to bring this up with your doctor

Name it. This is the one headache where saying the words changes everything: "I think this might be cluster headache." It steers the visit away from the default migraine assumption that costs people years.

Bring the specifics that define it. The attacks are on one side, around one eye; they last under three hours; the eye goes red and waters and the nostril blocks on that side; you cannot keep still during them; and they come daily, often at the same time, sometimes waking you. Bring the log of attack times against your sleep — the rhythm is persuasive.

What to ask for.

• Whether this fits cluster headache or another trigeminal autonomic headache, and whether a referral to a neurologist or headache specialist is warranted.

• Whether you can be prescribed the specific acute treatments — high-flow oxygen and injectable or nasal triptans — rather than oral painkillers.

• Whether preventive treatment through the bout is appropriate.

• What to avoid during a bout (alcohol above all).

If you are brushed off with "it's migraine" but the attacks are short, one-sided with a red watering eye, and leave you pacing, ask directly for that to be reconsidered or for a specialist referral. This condition is under-recognised enough that a clear, specific description from you genuinely shifts the outcome.

How we made it

Written from the International Classification of Headache Disorders (3rd edition) for the diagnostic criteria and the male-predominance and trigger statements, plus guidance from the American Migraine Foundation on acute treatment, a meta-analysis of the circadian pattern, and published studies on misdiagnosis and diagnostic delay. Where a belief is common but wrong — that this is a bad migraine, or a sinus or dental problem — we say so.

Written by the Welltory science team Data analysis by the Welltory data team Reviewed by Anna Elitzur, MD

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