It’s believed that migraines are caused by the changes in the chemicals of the brain, especially serotonin. During a migraine attack the level of serotonin decreases, which might cause a spasm in the blood vessels of your brain. This sudden spasm or contraction makes the blood vessels narrower causing the symptoms of aura. Soon after, the blood vessels dilate causing the headache. The exact reason for this sudden drop in the level of serotonin is still not known. 

Apart from serotonin, hormones are believed to be another reason behind the condition. The fluctuating levels of hormones during menstrual cycles are a close link to migraines. Some women experience migraines around the time of their periods, which is referred to as menstrual migraine. The fall in the level of estrogen causes this condition.

Menstrual migraines can either begin two days before the first day of a period or three days after the first day of a period. About one in seven women have migraine attacks only during their periods. This is known as pure menstrual migraine. The rest of the women have migraines at other times too.

There are also some factors like emotional, physical, dietary, environmental and medicinal factors that might trigger migraine attacks. 

Some of the emotional triggers can be:

• Stress
• Anxiety
• Tension
• Shock
• Depression
• Excitement

Some common physical triggers are:

• Fatigue
• Poor quality of sleep
• Shift work
• Poor posture
• Neck or shoulder tension
• Traveling for a long time

Dietary triggers can be:

• Irregular meals
• Lack of food or dieting
• Dehydration
• Alcohol
• Tyramine, found mostly in aged foods, such as cheese and wine.
• Caffeine products such as tea and coffee
• Specific foods such as citrus fruits, cheese and chocolates

Eating irregular meals causes blood sugar levels to drop. If you then eat something with sugar in it, the blood sugar level will immediately shoot up. This rise and fall could also trigger migraine attacks.

Environmental factors can also trigger migraine attacks such as:

• Bright lights
• Flickering screen
• Smoking or rooms full of smoke
• Loud noises
• Changes in climate, such as changes in humidity or very cold temperatures
• Strong smells
• Stuffy atmosphere

Some medicines are also capable of triggering migraines such as:

• Some types of sleeping pills
• Contraceptive pills
• Hormone replacement therapy (HRT), which is used to treat menopause

Migraines can also be a result of genetics. The condition tends to run in families although it isn’t necessary that everyone in your family will have migraine.