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Using a relevant example, describe how an allergic reaction occurs in a human being.

Answer Text:
- Allergy is a hypersensitive response by the body’s immune system to an antigen. The body immune system responds by overproducing
antibodies against harmless antigens to counter its effect. Antigen antibody reaction takes place on the surface of body cells that burst open
releasing a chemical substance called histamine.
Histamine causes inflammation, itching, swelling and pain in tissues. It also causes increased permeability of epithelial tissues causing them to draw in fluids/water hence swells up leading to narrowing lumen of structures like trachea, bronchus, and bronchioles. When airways constrict, they
allow little air through them producing a whizzing sound hence difficulty I breathing. This causes asthmatic attack. Histamine causes itching,
Redding and feeling warm/hot on a particular part of the body. Allergic response to substances like pollen, dust, animal fur, mite, particular foods
and emotional disturbance may provoke an attack. To counter the effect of histamine, antihistamine substances are administered.