“Allergies” is a general term that refers to a reaction the body has to allergens. Allergens are substances that are generally not harmful to the body. However, if you have allergies, the immune system thinks allergens are dangerous and tries to fight them off like it would any other intruder, such as bacteria, viruses, and parasites. Having allergies, therefore, means the immune system is overactive. In other words, the immune system is doing something it is normally supposed to do but the reaction is exaggerated, unnecessary, and even harmful to the body. In medical terminology, this overreaction is called a hypersensitivity reaction type 1.
There are many different kinds of allergies that differ based on the part of the body affected and the severity of symptoms. In some cases, allergies may cause a small rash, itchy eyes or a runny nose. In other cases, allergies can be life-threatening. Types of allergies include, but are not limited to, allergic rhinitis (inflammation in the nose), contact dermatitis (an allergic reaction on the skin), allergic asthma (a specific type of asthma), allergic conjunctivitis (irritation of the eye lining) and anaphylaxis (a life-threatening condition that involves swelling of the airways).