Allergy is a hypersensitivity reaction towards a normally harmless substance. Whenever we are exposed or our body is irritated by any external agent or so called allergen, our body becomes vulnerable and reacts to get rid of it. Externally, it is reflected in the form of known symptoms like sneezing, itching, swelling, pain, redness etc. However, these symptoms are the resultant effect of cascade of reactions taking place within our body. This happens because our body’s defense mechanism becomes ready to fight with the allergen and throw it out of the body.

The mechanism initiates by the activation of IgE antibodies which tend to bind on the surface of mast cells. This process results in releasing of various chemical mediators that are responsible for producing local inflammation. ‘Histamine’ is one of the many chemical mediators released and performs two important functions to induce inflammation. Firstly, it promotes vasodilation which is relaxation of the blood vessels to allow easy flow of the white blood cells so that they can aggregate at the site of inflammation and fight the infection. Further, this vasodilation of the peripheral capillaries allows the plasma to escape through its walls which accumulates in the surrounding tissue space. These reactions results into various symptoms of allergy depending upon the part of the body affected.

Most of the symptoms of allergy are elicited in the form of inflammation and itch. Inflammation, denoted by suffix 'itis'. e.g. in Arthritis, Spondylitis, Tonsillitis, Pharyngitis, Rhinitis, Gastritis etc. is manifested as pain, swelling, redness, rise in temperature and loss of function of the affected organ.

Allergy mainly affects 4 systems i.e. Skin, Respiratory System, Gastrointestinal system and Musculoskeletal System. The various manifestations of these inflammatory reactions for each system are represented below: