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Allergy is a disorder of the immune system which is a form of hypersensitivity. Allergic reactions occur to normally harmless environmental substances known as allergens; these reactions are acquired, predictable, and rapid. Strictly, allergy is one of four forms of hypersensitivity and is called type I (or immediate) hypersensitivity. It is characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response. Common allergic reactions include eczema, hives, hay fever, asthma attacks, food allergies, and reactions to the venom of stinging insects such as wasps and bees.

Mild allergies like hay fever are highly prevalent in the human population and cause symptoms such as allergic conjunctivitis, itchiness, and runny nose. Allergies can play a major role in conditions such as asthma. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening anaphylactic reactions.

A variety of tests now exist to diagnose allergic conditions; these include testing the skin for responses to known allergens or analyzing the blood for the presence and levels of allergen-specific IgE. Treatments for allergies include allergen avoidance, use of anti-histamines, steroids or other oral medications, immunotherapy to desensitize the response to allergen, and targeted therapy.

Definition:

An allergy is an exaggerated immune response or reaction to substances that are generally not harmful.

See also:

1. Hay fever (allergic rhinitis)

2. Food allergies

3.Allergy testing

4.Contact dermatitis

5.Atopic dermatitis (eczema)

6.Allergy to mold, dander, dust

7.Allergy testing

8.Allergic reactions

9.Allergic conjunctivitis

Allergies are abnormal immune system reactions to things that are typically harmless to most people. When you’re allergic to something, your immune system mistakenly believes that this substance is harmful to your body. (Substances that cause allergic reactions, such as certain foods, dust, plant pollen, or medicines, are known as allergens.)

In an attempt to protect the body, the immune system produces IgE antibodies to that allergen. Those antibodies then cause certain cells in the body to release chemicals into the bloodstream, one of which is histamine (pronounced: his-tuh-meen).

The histamine then acts on the eyes, nose, throat, lungs, skin, or gastrointestinal tract and causes the symptoms of the allergic reaction. Future exposure to that same allergen will trigger this antibody response again. This means that every time you come into contact with that allergen, you’ll have an allergic reaction.

Allergic reactions can be mild, like a runny nose, or they can be severe, like difficulty breathing. An asthma attack, for example, is often an allergic reaction to something that is breathed into the lungs by a person who is susceptible.

Some types of allergies produce multiple symptoms, and in rare cases, an allergic reaction can become very severe — this severe reaction is called anaphylaxis (pronounced: an-uh-fuh-lak-sis). Signs of anaphylaxis include difficulty breathing, difficulty swallowing, swelling of the lips, tongue, and throat or other parts of the body, and dizziness or loss of consciousness.

Anaphylaxis usually occurs minutes after exposure to a triggering substance, such as a peanut, but some reactions might be delayed by as long as 4 hours. Luckily, anaphylactic reactions don’t occur often and can be treated successfully if proper medical procedures are followed.