Common migraine is a disorder involving recurrent headaches, which may be accompanied by symptoms other than headache but which rarely include a preliminary warning (called an aura).  Migraine headaches affect about 6 out of 100 people.  They are a common type of chronic headache.  They most commonly occur in women and usually begin between the ages of 10 and 46.  In some cases, they appear to run in families.  Migraines occur when blood vessels of the head and neck spasm or constrict, which decreases blood flow to the brain.  Minutes to hours later, the blood vessels dilate (enlarge), resulting in a severe headache.  Inflammation around the blood vessels also occurs in some cases.  Common migraine may be accompanied by symptoms other than headache but only rarely includes any preceding symptoms (aura).  Migraines may also appear as classic migraine (a migraine preceded by other symptoms) and other rare forms.  Multiple mechanisms trigger the spasm and subsequent blood vessel dilation.