@explainique: Histamine does much more than cause allergies. H1 receptors are involved in allergy symptoms like itching, sneezing, hives, and watery eyes. H2 receptors help control stomach acid. H3 receptors influence brain signalling, wakefulness, and neurotransmitter release. H4 receptors are involved in immune cell activity and inflammation. Simple idea: histamine has different receptors — and each one affects a different part of the body. #Histamine #Allergies #Pharmacology #Immunology #HealthcareEducation