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 know