A headache could be caused by anything. Triggers don’t actually cause the pain. Instead, they activate an existing imbalance in your brain. Doctors don’t completely understand how triggers work. Keeping a headache calendar is one way of identifying a pattern in the things you do, eat or feel and the onset of a headache. If you do identify a pattern, you can try to avoid those factors that seem to cause your headaches and see what happens.

The most common headache triggers include:

• Stress, Particularly for chronic tension headaches or migraine, stress can be a powerful trigger. Such stress may come from major life events such as a divorce or moving. Constant "daily hassles" can have an even bigger effect.
• Some suggest that stress increases a pain–producing imbalance by enhancing the pain carrying pathways in the brain and inhibiting the brain’s own internal pain control system.
• Diet A small percentage of people with migraine point to a particular food as a factor in their attacks. Alcoholic beverages, especially red wine and beer, may cause problems. Congeners, the substances that give an alcoholic beverage its distinguishing characteristics, may be a culprit rather than the alcohol itself.

Chocolate may be another trigger. But it’s not clear whether chocolate causes migraine or whether a sudden craving for chocolate is an early symptom of an impending migraine.
Caffeine withdrawal can cause headache. When blood levels of caffeine drop, symptoms of withdrawal, including headache, may set in. That’s why heavy coffee drinkers commonly experience “Morning headache” until they have that first cup of coffee, and why many people who sleep in late on the weekends have a headache on those days.
Food additives, such as sodium nitrite and monosodium glutamate in many processed foods, may also trigger migraine in some people.

Other common triggers are:

• Change in the weather or seasons, altitude, or time zones.
• Change in sleep patterns and meal times.
• Fluctuations in hormone levels during the menstrual cycle or pregnancy, estrogen therapy for menopause, or use of oral contraceptives.
• Sensory irritants, such as strong or flickering lights, or unusual odors.
• Polluted air or stuffy rooms.

Anti–depressants are sometimes given to people with migraine even if they aren’t depressed. Certain antidepressant medications can also be very helpful in chronic tension headaches as well as migraines.