Histamine

Histamine is a signaling molecule stored in mast cells and basophils and released during allergic reactions, where it widens blood vessels and triggers itching and swelling.

The body makes histamine from the amino acid histidine and keeps most of it packed in granules inside mast cells, which sit in skin, airways and the gut lining. When an allergen cross-links antibodies on those cells, the granules empty and histamine acts on four receptor types: H1 drives itch, hives and airway narrowing; H2 stimulates stomach acid; H3 regulates neurotransmitter release in the brain; H4 guides immune-cell movement. Antihistamines sold for allergies block H1, and older ulcer medicines block H2. Histamine also acts as a neurotransmitter that promotes wakefulness, which is why first-generation antihistamines cause drowsiness.

Readers meet the term in allergy, mast cell activation and histamine intolerance discussions. Whether CBD changes histamine release in people is an open research question; laboratory findings exist, but no human evidence shows that CBD lowers histamine, and it should not be described that way.