While this is a helpful response, it also causes redness, swelling and itching.
Read the leaflet that comes with your particular brand for further information.
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.
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.
For example: For other conditions, specific antihistamines may be used.