When Is a Headache Serious? The Red Flags Doctors Look For
Most headaches are harmless. A doctor explains the warning signs that need urgent attention, migraine versus tension headache, and how painkillers cause headaches.
Key takeaways
- Over 90 percent of headaches are migraine or tension-type and do not need a scan.
- A sudden 'worst ever' headache, a headache with fever and stiff neck, with weakness or confusion, after a head injury, or a new headache after 50 needs urgent assessment.
- Taking painkillers on more than ten to fifteen days a month causes medication-overuse headache, one of the commonest reasons for daily headache in India.
- A headache diary for four weeks tells a doctor more than most scans do.
Headache was the most searched symptom in India in 2025, and the search usually ends in one of two mistakes: dismissing a headache that needed attention, or spending a fortnight terrified about a tumour that was never there. Doctors sort headaches with a short list of warning signs. This guide gives you that list, explains the common headaches that make up almost every case, and tells you what to do about them.
How common is a serious headache?
Rare. In people who see a doctor for headache, well over 90 percent have migraine, tension-type headache or a headache caused by their own painkillers. Brain tumours, bleeds, infections and clots exist, and they matter, but they almost always come with clues. The purpose of the red-flag list is to catch those clues without scanning everyone.
The red flags that need urgent attention
Go to an emergency department, or call 108 or 112, if a headache is:
Sudden and severe, reaching its worst within a minute, sometimes described as the worst headache of your life. Accompanied by fever, a stiff neck, a rash or confusion. Accompanied by weakness, numbness, slurred speech, double vision, loss of vision or a seizure. Following a head injury, especially in someone on blood thinners or over 60. Accompanied by fainting or drowsiness that is hard to wake from. In pregnancy or the weeks after delivery, with high blood pressure or swelling.
Doctors also treat these as flags that need a prompt, though not emergency, assessment: a new headache starting after the age of 50; a headache that is progressively worse over days to weeks; a headache that is worse on lying down, on coughing, straining or bending, or that wakes you from sleep; a headache with a change in personality or memory; a headache in someone with cancer, HIV or on immunosuppressive treatment; and a headache that has clearly changed its pattern from what you usually get.
The mnemonic neurologists use is SNNOOP10: systemic symptoms, neurological signs, sudden onset, older age at onset, pattern change, positional, precipitated by exertion, papilloedema, pregnancy, painkiller overuse, and a few more. You do not need to memorise it; you need to recognise that a headache that is different, sudden or accompanied by something else is the one to take seriously.
The common headaches, and how to tell them apart
| Type | Feels like | Typical clues | What helps |
|---|---|---|---|
| Migraine | Throbbing, often one-sided, moderate to severe | Nausea, light and sound sensitivity, worse with movement, lasts 4 to 72 hours, sometimes visual aura | Early triptan or NSAID, dark quiet room, preventive medicine if frequent |
| Tension-type | Tight band around the head, mild to moderate | Both sides, no nausea, not worse with activity, linked to stress, posture, screens | Simple analgesic occasionally, stretching, sleep, stress management |
| Medication-overuse | Dull daily headache, often on waking | Painkillers on 10 to 15 or more days a month for 3 months | Stopping the painkiller under guidance; it gets worse before it gets better |
| Cluster | Excruciating, around one eye | Tearing, red eye, blocked nose on the same side, attacks in clusters at the same time daily, mostly men | Oxygen, injectable triptan, preventive treatment from a neurologist |
| Sinus | Pressure over cheeks and forehead with a cold | Nasal discharge, fever, worse bending forward | Treat the infection; true sinus headache is rarer than believed |
Most “sinus headaches” in India are actually migraine, and most “eye strain” headaches are tension-type. The treatment is different, so the label matters.
Migraine is the big one
One in seven people has migraine, and in India it is under-diagnosed and under-treated, partly because attacks are labelled acidity, gas, weakness or a weak brain. Migraine is a neurological condition with well-defined triggers: skipped meals, dehydration, poor or irregular sleep, hormonal changes around periods, bright light, strong smells, alcohol, and stress followed by relaxation. It is not caused by the eyes, the stomach or a personality.
Two things change its course. The first is treating attacks early, at the first sign, with an adequate dose rather than waiting to see how bad it gets. The second is a preventive medicine when attacks come four or more days a month or are disabling; several inexpensive options exist and a neurologist or physician can choose one to suit you. Newer antibody treatments are available in India for people who do not respond.
Painkillers that cause headaches
This is the most under-recognised cause of daily headache. Taking any painkiller, including paracetamol, combination tablets, NSAIDs and especially those containing caffeine or codeine, on more than ten to fifteen days a month for a few months causes the brain to produce headache as the medicine wears off. The person takes more, and the cycle tightens. The treatment is to stop the overused medicine, ideally with a doctor’s plan for the difficult first two weeks, and to start a preventive. Most people are dramatically better within two months.
If you buy strips of painkillers routinely, count the days. Ten a month is the ceiling.
What a doctor actually does with a headache
Takes a history: when it started, how it builds, where it is, what comes with it, what you take for it, and what your usual headache is like. Examines you: blood pressure, the back of the eye for pressure signs, the neck, and a brief neurological check. That takes ten minutes and determines whether a scan is needed. A scan is ordered when there is a red flag or an abnormal finding, not because the headache is bad. Bad headaches are usually migraine; dangerous ones are usually different.
If a scan is ordered, the MRI report guide explains what the words mean.
What you can do this month
Keep a headache diary for four weeks: date, duration, severity out of ten, what you took, and possible triggers such as sleep, meals and periods. Count painkiller days. Fix sleep timing. Do not skip meals. Reduce caffeine gradually if you drink a lot. Then see a doctor with the diary. It is the single most useful thing you can bring.
When to see a neurologist
See any doctor promptly for the flags above. See a neurologist if headaches occur four or more days a month despite basic measures, if you have failed two or three preventive medicines, if attacks are unusual, such as cluster headache or prolonged aura, or if there is any neurological symptom between attacks. Headache is one of the most treatable conditions in neurology; the tragedy is how long people put up with it.
Frequently asked questions
Should I get an MRI for my headaches?
Only if there is a red flag or an abnormal examination. Scanning a typical migraine finds nothing useful in the vast majority of cases and often turns up harmless incidental findings that cause anxiety. A doctor decides this after taking a history and examining you, which is why the consultation matters more than the scan.
How do I know if my headache is a migraine?
Migraine is usually one-sided or throbbing, moderate to severe, worse with movement, and comes with nausea or sensitivity to light and sound. Attacks last four hours to three days. If a headache regularly stops you working or makes you want to lie in a dark room, it is probably migraine, and it is treatable.
Can high blood pressure cause headaches?
Ordinary high blood pressure rarely does. Very high readings, above about 180/120, can cause headache and are an emergency. A headache in someone with normal or mildly raised pressure is almost never caused by the pressure.
Why do I get a headache every day?
The commonest reasons are medication-overuse headache from frequent painkillers, chronic migraine, poor sleep, untreated sleep apnoea, caffeine withdrawal and neck strain from screens. A daily headache that is new, progressive or worse on lying down needs a doctor promptly.
Are eye problems a common cause of headache?
Less often than people assume. Uncorrected vision can cause eye strain and a mild headache after close work, and an eye test is reasonable, but most headaches attributed to the eyes are migraine or tension-type.
Sources
- NICE guideline CG150: Headaches in over 12s, diagnosis and management
- NHS: Headaches
- Do TP, et al. Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list. Neurology. 2019
- International Classification of Headache Disorders, 3rd edition
- World Health Organization: Headache disorders fact sheet
This guide is for general education and reflects the evidence available on the last reviewed date. It is not a diagnosis, a prescription or a substitute for seeing a doctor who can examine you. If you have symptoms that worry you, or the guide tells you to see someone, please do. Full disclaimer.