The term ‘allergy’ talks about a reaction of an altered tissue after it is brought in contact with an antigen also called an ‘allergen‘. The allergic reaction generally occurs when the body tissues are sensitive to the allergen and they tend to react to foreign invaders. The allergen comes in contact with the tissues in various ways. It could be through direct contact with the skin or through mucous membranes of the organs or even through the bloodstream.

Various Types of allergens:

External Allergens: pollens, dust, cosmetics, and animal hair; poisonous plants, serums, vaccines, and drugs.