MAST CELL ACTIVATION SYNDROME (MCAS) & ME/CFS MCAS is a condition where mast cells - immune cells that normally help protect the body - become overactive. When triggered, they release chemicals such as histamine, which can cause a wide variety of symptoms across different body systems, many of which overlap with ME/CFS symptoms. Whilst The BMJ describes MCAS as rare, the Bateman Horne Center suggests it is a common comorbidity in ME/CFS and long COVID (although more robust research is needed to confirm a link). mast cell • . • brain fog fatigue itchiness urticaria (hives) INFORM. INFLUENCE. INVEST. ( dizziness palpitations wheezing nausea bowel issues 141% RESEARCH UK SCO36942