Sedating antihistamines and asthma
Antihistamines work by physically blocking the H1 receptors, stopping histamine from reaching its target.This decreases your body's reaction to allergens and therefore helps to reduce the troublesome symptoms associated with allergy.Anaphylaxis usually occurs minutes after exposure to a triggering substance, mainly associated with food allergies, such as a peanuts or shellfish, but some reactions might be delayed by as long as 4 hours.
This excessive release of histamine produces the associated symptoms of itching, swelling, runny eyes, etc.
Antihistamines are a group of medicines which act by blocking the action of the chemical called histamine in the body.
Either H1 or H2 histamine receptors can be blocked by medicines, but the group commonly known as antihistamines blocks the H1 receptor.
These effects are mainly caused by the older first-generation antihistamines which are described below.
Note: antihistamines should not be confused with H2 blockers which reduce the production of stomach acid.
While this is a helpful response, it also causes redness, swelling and itching.