Classification Migraines have been classified by the International Headache Society which periodically revises their classification.  Defining severity of pain In addition to classifying the type of headache, the International Headache Society defines intensity of pain on a verbal 4 point scale:
0 no pain 1 mild pain 'does not interfere with usual activities'
2 moderate pain 'inhibits, but does not wholly prevent usual activities'
3 severe pain 'prevents all activities' 
Migraine without aura This is the most commonly seen form of migraine; patients who primarily suffer from migraine without aura may also have attacks of migraine with aura. According to the International Classification of Headache Disorders it is a recurrent headache disorder manifesting in attacks lasting 4-72 hours. Typical characteristics of the headache are unilateral location, pulsating quality, moderate or severe intensity, aggravation by routine physical activity and association with nausea and/or photophobia and phonophobia. In order to diagnose migraine without aura, there must have been at least five attacks not attributable to another cause that fulfill the following criteria:
1. Headache attacks lasting 4-72 hours when untreated
2. At least two of the following characteristics: Unilateral location Pulsating quality Moderate or severe pain intensity Aggravation by or causing avoidance of routine physical activity
3. During the headache there must be at least one of the following associated symptom clusters: Nausea and/or vomiting Photophobia and phonophobia Where these criteria are not fully met, the problem may be classified as "probable migraine without aura" but other diagnoses such as "episodic tension type headache" must also be excluded.