11/11/2025
MCAS and histamine intolerance are often confused, but they are not the same.
MCAS happens when mast cells become unstable and release multiple inflammatory chemicals, causing system-wide symptoms in the skin, gut, sinuses, bladder, heart rate, brain, mood, and sleep. It has many triggers including heat, stress, hormones, infections, chemicals, smells, medications, alcohol, exercise, temperature changes, and food.
Histamine intolerance (HIT) is different. The body cannot break down histamine well, so histamine from food builds up. HIT is mainly food-triggered, and symptoms are mostly gut-related such as bloating, nausea, reflux, diarrhea, flushing, and headaches.
In short, MCAS is multi-system and multi-trigger. HIT is mostly food-related.