Histamine plays a key role in the body's immune response and is primarily involved in local immune reactions. It is released by immune cells such as mast cells and basophils during allergic reactions, causing symptoms like itching, swelling, and increased mucus production. Because of this, histamine is central to conditions like hay fever, asthma, and hives. In pharmacology, histamine is used in research and diagnostics. It helps assess bronchial responsiveness in asthma through challenge tests. It also stimulates gastric acid secretion and has been used historically to study stomach function, though this application is now limited. Drugs that block histamine's action—antihistamines—are widely used to treat allergies, motion sickness, and insomnia. Conversely, compounds that influence histamine pathways are being explored for neurological conditions, as histamine acts as a neurotransmitter in the central nervous system, regulating wakefulness and appetite.