An allergy is an abnormal reaction or increased sensitivity to certain substances. The allergic individual produces symptoms when exposed to these substances, which are harmless to non-allergic people.

Normally, the body's defence system fights against foreign bodies. In most allergic reactions, it is a false alarm which induces the body’s defence mechanism to fight against the substance.

The prevalence of allergic diseases has been increasing and both genetic and environmental factors play a role in creating allergic symptoms.