You may be familiar with histamine if you take antihistamines for hay fever or allergies. It's a chemical that is released when the immune system feels under attack. It causes an immediate inflammatory response, expanding the blood vessels so that white blood cells can flood the bloodstream and find the source of the attack.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/is-a-histamine-intolerance-to-blame-for-your-migraines