While headache is frequently regarded as a condition in its own right, it can often be a symptom of an underlying problem. For this reason, headaches are categorised as either primary or secondary:

1. Primary headaches

These are not associated with another medical condition. Examples include migraine; tension headaches; cluster headaches; and headaches that have a very definite trigger, for example those that are caused by a cold stimulus, such as eating an ice cream, or arise as a result of coughing

2. Secondary headaches

These have an underlying cause, for example, a bleed on the brain; injury to the head or neck; increased pressure within the skull because of hypertension or a brain tumour; an infection such as meningitis; or a disorder of one of the facial or cranial structures, such as sinusitis or acute glaucoma. Headaches that stem from either exposure to or withdrawal from a substance also fall under this classification. For example, taking cocaine or inhaling carbon monoxide can cause a headache and alcohol consumption causes dehydration which can also lead to a headache. A headache may also occur because of a nerve problem, such as trigeminal neuralgia.

Headache is one of the most common reasons for making an appointment to see a GP. Taking into consideration the fact that most people do not do this and instead try and sort out their headache on their own, the scale of the problem quickly becomes clear. 

It is believed that around nine in every 10 headaches fall into the primary category, and so this module will largely focus on these.