Long list. Certain food, items, or fasting, hormonal changes, lack of sleep, certain smells bright lights, fatigue and a host of other environmental factors often unique to the individual.
Internal Controls. Migraine=vascular, in this case the arteries within the meningeal membranes surrounding the brain. Always under mind/brain control, like all the arteries. A period of constriction of the arterial wall muscles (vasospasm) is followed by relaxation & arterial BP enlarges the arteries stretching the walls & the surrounding & exquisitely innervated, pain sensitive meningeal membranes, a painful pulse.
External & internal. Foods (red wines, aged cheeses, nitrites, msg), bright sunshine or indoor lighting, intense alternating colors (black and white stripes). Strong odors (perfumes, fishy smells), changes in atmospheric pressures or fronts, stress (especially afterwards when relaxing), irregular sleep habits, infections and high temperatures. Body, such as tmj, sinus, thoracic outlet, neck issues.