Organisms when come in contact with substances like allergens through eyes, skin, nose, gastrointestinal tract, respiratory tract etc. and produce reactions, they are called allergic reactions. Allergens can be swallowed, injected or breathed into the lungs. Occurrence of allergic reactions is very common. They may happen soon after an organism comes in contact with an allergen. These reactions may be mild or could be severe, life threatening even. They may be limited to specific area of a body or they may affect the entire body. The severest form of an allergic reaction is termed as anaphylaxis or anaphylactic shock. A person having a family history of allergies is more prone to suffer from such reactions. An initial exposure may produce only a mild reaction. But, a repetition of such conditions can lead to more serious reactions. Once an individual is sensitized, i.e. has had an exposure or allergic reaction, even a small amount of allergen or a very limited exposure can trigger a severe reaction.