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What causes headaches?

My migraines, which fortunately occur only once a year, start with huge zigzag lines across my field of vision.

Only once did a migraine occur in the middle of surgery. The only way I could see the computer screen was to close one eye and look up from a stooped position. Apart from the zigzags, I was fine. The waiting room was full, so I carried on. However, the 8-year-old boy next in found it immensely funny to find his GP seemingly doing an impersonation of Quasimodo. He decided to copy me for a while, so we stood there eye to eye, until his mother came in and the spell was broken. I tell this story simply to demonstrate that no one is immune to headaches, not even doctors.

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'Not tonight dear, I have a headache'

Believe it or not, there is an International Headache Society. The IHS have taken it upon themselves to classify headaches. This is dandy for them, but a real, erm, headache for those of us who have to remember it all.

Strangely, the 'avoidance of sex' headache doesn't get a mention, but lots of other weird ones do.

Let's try to make sense of it all. The IHS break headaches down into two main types - primary and secondary. Primary headaches have no underlying illness, whereas secondary headaches are always the result of some other mischief going on.

Primary headaches

The good news is that 90% of headaches are of the primary type. This means if you're worried that your headache is a sign of serious disease, the odds are in your favour.

If that's all you wanted to know you can stop reading now and go off and watch Strictly or something, but I would advise you to stick with it. There is some pretty mind-blowing stuff coming up.

The good old tension-type headache tops the list of primary headaches. It typically feels like a tight band around the head and is due to the muscles of the scalp going into spasm in reaction to stress. The story about the man who was cured of 'tension headaches' when his doctor told him to buy a larger hat may be an urban myth, but it gives you some idea of what it feels like.

Migraine headaches are the mummy (or daddy?) of all primary headaches. You can get a throbbing pain on one side of the head, with nausea and sometimes actually being sick. If that wasn't enough your eyes can go funny, with zigzag lines, flickering lights or blind spots. It's disabling enough to bring down an adult GP in full flight (see above).

Cluster headaches also occur on one side of the head but you often get several attacks together and then a period of months or even years without any symptoms at all. You may notice watering and redness of the eye, partial closure of the eyelid and a blocked nose.

"There's severe stabbing, knife-like pain, which could last up to around three hours in duration," said Dr Teshamae Monteith, assistant professor of clinical neurology at the University of Miami and member of the American Academy of Neurology. "They can happen multiple times during the day, often right before you go to bed and sometimes in the middle of the night, at around 4 am."

Other types of primary headache

There's a whole ragbag of primary headaches which occur occasionally. I reckon the IHS gave up at this point and just listed headaches according to when they occurred, or what symptoms were associated with them. So there are headaches that are brought on after exercise, headaches associated with having sex, and headaches caused by coughing.

Some headaches can be quite dramatic. There's 'thunderclap headache', a sudden severe headache that can last from hours to days, which mimics the pain you get with a brain haemorrhage; hemicrania continua, which is a bit like cluster headaches but you get them every day for three months; and 'ice pick' headache (primary stabbing headache) which causes a single stab or series of stabs in the head.

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Secondary headaches

Secondary headaches always have an identifiable underlying cause. Headache associated with taking too much medication is a common type. It's called medication-induced headache (sometimes called 'medication overuse headache'). People get into a vicious cycle of taking headache treatment but the medication itself can make the headache worse. Paracetamol or ibuprofen are often the cause but a lot of other types of medication taken for headaches may also be involved. Eventually the headache comes back when the medicine is stopped, so people end up taking tablets just to stop the headache from coming back.

OK, it's time to get the serious stuff over with. Brain tumours, brain haemorrhage, meningitis and giant cell arteritis (an inflammation of the arteries on the sides of the head) can all cause headaches. They are the conditions we all fear when a nasty headache lingers. However, the good news is that the chances of any headache having a serious cause are very slim indeed.

Surprising causes of headaches

What delicate flowers we are. Too much sleep, too little sleep, too much fluid (all right, too much alcohol), not enough fluid (dehydration), too much of the wrong food or no food at all can all trigger migraines in susceptible people. Depression, certain smells, the weather, and being obese have all been linked to migraines. Don't overwork, because that causes migraines, but don't relax, because a reduction of stress can cause - guess what? - migraines.

But if you get fed up looking for trigger factors, just blame it on your family. Dr Aarno Palotie, a geneticist at the University of California, in Los Angeles, said: "For the first time we have proof of an isolated genetic link to migraine." He and his team are close to isolating the genes associated with some forms of migraine.

Stuff we put in our bodies in various orifices, which can cause generalised headaches, include foods containing sulfites (anything smoked - like salmon, alas), oral contraceptives, amyl nitrite (as in 'poppers'), cannabis and nicotine.

For migraine sufferers, caffeine can be a major trigger for bringing on headaches, and for developing chronic migraine (defined as headache on at least 15 days per month, with at least 8 being migraine or probable migraine). But if you fancy a coffee at the end of your meal (tyramine-low, of course) don't stop drinking it immediately because caffeine withdrawal can be another headache trigger.

By now, you're probably getting a headache just trying to avoid all these headache triggers. Time for a nightcap? Best not. Alcohol not only gives you a hangover but can also cause instant headache due its effect on brain blood vessels. Maybe just go straight to bed. Oh, before you do, check your boiler. Headache can be one of the first symptoms of carbon monoxide poisoning.

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When should I bother my doctor?

It's a real headache, isn't it? On the one hand, you don't want to risk bothering your GP with something as 'trivial' as a headache. On the other hand, if it is something serious, you don't want to leave it. Fortunately, our headache leaflet has it covered. Look on there for all the details, but basically, if it starts suddenly; if it becomes severe; if it wakes you from sleep; if it's worse when you're lying down and gets better when you stand; if you get odd symptoms (eg, memory loss, muddled thinking, speech problems, vomiting); or signs (fever, red eyes, numbness or weakness you've never had), go to see your doctor.

Likewise, if you've had a head injury in the previous three months, if your headache is made worse by actions that increase the pressure in your head such as coughing or sneezing, if you have a condition likely to increase the risk of infection (eg, HIV) or a type of cancer that can spread, your doctor should be informed.

What should I do if I get a headache?

C'mon, do you really expect me to cover the treatment of all types of headaches in this little bit of space I've got left? Needless to say, all the details can be found in our headache leaflet. Many headaches disappear by themselves but those that linger can usually be encouraged on their way by resting and taking some paracetamol. It's worth looking at the various possible trigger factors to see whether any apply to you and even keeping a diary of your activities and diet to help identify them.

If you get frequent headaches, it's important that you should be diagnosed properly. Some types of headaches require specific types of treatment when they occur, and measures to prevent them from happening. Identifying and avoiding trigger factors is particularly important.

To end on a note of hope, if you've been on medication for years and it's not totally effective, don't despair. Advances in therapy are coming on stream all the time. For example, new preventative treatments are being developed in America. They target a specific group of amino acids in the brain. "They have an enormous potential to change the lives of headache patients," says Dr Rebecca Burch, a headache specialist at the John R. Graham Headache Center at Brigham and Women's Faulkner Hospital in Boston.

Are you starting to see zigzag lines or is it just me? If you can, you might need to get your eyes tested. Me? I'm off to lie down in a darkened room.

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The information on this page is peer reviewed by qualified clinicians.

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