MCAS involves inappropriate or excessive activation of mast cells, leading to unpredictable histamine release and a wide array of symptoms such as flushing, brain fog, bloating, fatigue, itching, and rapid heart rate. Histamine intolerance, on the other hand, results from an imbalance between histamine intake or production and the body’s ability to break it down, often due to impaired DAO (diamine oxidase) enzyme activity. Both conditions are often underrecognized and misdiagnosed, but identifying patterns across body systems—and understanding the histamine connection—can lead to targeted relief and deeper healing.