WHAT IS IT?
A headache is any pain in your head. This may sound obvious, but sometimes it can be difficult to work out exactly where the pain is coming from. Problems with your sinuses, for instance, can cause pain over your forehead and the front of your face, and dental problems can cause pain in your jaw and your ear.

WHAT COULD IT BE?
It is worth remembering that headaches are very common, and that non-serious causes of headache are much more common than serious ones. However, you are much more likely to have something to worry about if you get a headache which is unlike any you have had before, or if it is much more severe than you have had before. Possible causes include:

Recurrent or chronic headaches
- Tension headache. This is a very common cause of headache. It tends to be present all day, and is worse towards the evening or when you are feeling very stressed. It may feel like a tight band around your head, or move up from the back of your neck to your temples. It is not usually associated with other symptoms like flashing lights or vomiting. It is usually due to your muscles going into spasm because you are tense. Painkillers may not help, and can actually make it worse. The best way to get rid of it is to try and relax - rest, massage, pampering yourself or even physical exercise can all help.

- Migraine. This kind of headache often affects only one half of your head. You may feel sick or vomit, and the pain may be preceded by an "aura", with flashing lights, zigzag lines in your field of vision, pins and needles, numbness or weakness in one side of your face or body. It tends to run in families and may be brought on, or made worse, by being premenstrual or by taking the combined oral contraceptive pill. If your migraines suddenly start or get worse, or if you start developing other symptoms in one part of your body (like weakness or problems with your eyesight) when you are taking the combined oral contraceptive pill, you should seek medical help as soon as possible.

- Eye strain commonly causes headaches around your eyes, especially when you have been doing a lot of close work or spending a lot of time on the computer. The pain may be associated with temporary blurred vision, but tends to settle with painkillers or stopping work. If you think this is your problem, make an appointment with your optician and take regular breaks from work.

- Cluster headaches. These are commoner in men than in women (especially between the ages of 35 and 45). They are always on one side. The pain often comes on at night - it starts suddenly and becomes very severe around one eye. This eye may become watery, inflamed and bloodshot. The pain lasts for 20-60 minutes and comes back regularly for several days or even weeks. If you think you have cluster headaches, you should make an appointment with your GP.

- Side effects of medication. Some medicines, such as blood pressure tablets or angina treatments, can cause headaches. The big clue is that they tend to start at the same time as you started your medicine. Talk to your GP - he may change your treatment, or reassure you that they will settle in time.

- Temporal arteritis. This cause of headache is rare under the age of 50, and is usually associated with pain over your temples and tenderness in the same area. It can cause serious problems if not treated early, but responds very well to steroid tablet treatment.

One-off headaches
- Hangover. The combination of dehydration and toxins left in your body can cause a nasty headache after a bout of drinking. Of course, the best way to avoid it in the future is not to drink too much at one sitting, but you can also help by drinking plenty of water before you go to bed.

- Virus infection. Many virus infections cause headache as well as muscle aches, fever, tiredness and general "grottiness". They tend to settle with simple painkillers, rest and plenty of fluids.

- Sinusitis. This may feel like a headache, affecting you forehead and cheeks. It is worse when you bend forward and when you wake up in the morning. You may also have foul-smelling yellow or green discharge from your nose and a feeling of dripping down the back of your throat. Antibiotics usually don't help much - try steam inhalations and simple painkillers first. If the pain is severe and doesn't settle in a few days, make an appointment with your GP.

- Meningitis in adults classically causes fever, a severe headache, pain in the back of your neck and a dislike of bright lights (see section on Meningitis). You will probably be very ill, and the headache will probably get worse and worse. As a late sign, you may develop small dark red/purple spots under your skin, which do not fade when you press a glass against them. If you are worried about meningitis, seek medical help immediately. If you are in doubt, you can call NHS Direct on 0845 46 47 for advice.

- Subarachnoid haemorrhage is caused by a burst blood vessel in your brain. The headache comes on very suddenly, and is usually "the worst headache I've ever had". Before it happens, you may be entirely well, but the headache may be accompanied by vomiting, weakness in part of your body, drowsiness and loss of consciousness. Seek medical help immediately.

- Severely raised blood pressure. Very high blood pressure can occasionally cause headache and blurring of your vision. This includes the raised blood pressure of pre-eclampsia in pregnancy, which can also cause ankle swelling, vomiting and pain in the top of your stomach. If you have any new headache which is very severe, especially if you are pregnant or it is accompanied by problems with your vision, you should seek medical help urgently.

- Brain tumour. The headache of brain tumour is caused by the pressure inside your brain being raised. It is severe and poorly localised. It is usually worse after you have been lying down and may wake you from sleep. It is not relieved by painkillers and you may have other problems such as blurred or double vision. Other causes of raised pressure inside your brain may give rise to the same symptoms. If you have a new, severe headache that is not relieved by painkillers, you should seek medical help. This is especially urgent if you have other symptoms affecting your eyes.

WHEN DO I NEED TO WORRY?
If your headache is occasional or recurring and responds to simple painkillers, there is usually no cause for concern. If you have a sudden severe headache (especially with other symptoms, see above), or if you have a headache which does not settle with time or simple painkillers, you should seek medical help, usually urgently (see above). Read through the list above - if your symptoms suggest you have something that needs medical attention, get it.

HOW CAN I HELP MYSELF?
Many of the most common causes of headache are either caused by, or made worse by, stress. You should look at your lifestyle and see how you can reduce your stress levels - relaxation techniques, yoga or regular exercise may help.
You should also make sure that you eat regularly, take a healthy balanced diet, drink plenty of fluids (except alcohol, coffee, tea and colas) and get enough sleep.