The exact cause of migraines is unknown, but they're thought to be the result of abnormal brain activity temporarily affecting nerve signals, chemicals and blood vessels in the brain.
It's not clear what causes this change in brain activity, but it's possible that your genes make you more likely to experience migraines as a result of a specific trigger.
Many possible migraine triggers have been suggested, including hormonal, emotional, physical, dietary, environmental and medicinal factors.
These triggers are very individual, but it may help to keep a diary to see if you can identify a consistent trigger.
It can also sometimes be difficult to tell if something is really a trigger or if what you're experiencing is an early symptom of a migraine attack.
Some women experience migraines around the time of their period, possibly because of changes in the levels of hormones such as oestrogen around this time.
These type of migraines usually occur between 2 days before the start of your period to 3 days after.
Some women only experience migraines around this time, which is known as pure menstrual migraine.
But most women experience them at other times, too, and this is called menstrual-related migraine.
Many women find their migraines improve after the menopause, although the menopause can trigger migraines or make them worse in some women.
Also, foods that have been stored at room temperature, rather than being refrigerated or frozen, can have rising levels of tyramine.