What is Allergy?

Reading time: 1 min

Allergy is a disorder of the immune system in which the defenses respond inappropriately and they identify external substances as harmful that, due to their nature, are inoffensive.  

The person with an allergy develops defenses (immunoglobulins) to certain substances, called allergens, to which they are exposed. The allergens can be substances or particles that they inhale (mites, pollens, animal skin flakes, etc.), foods, drugs, insect venom, contact elements (metals, perfumes, cosmetics, gums, etc.).

The clinical characteristics of the allergic disease differ as regards the type of hypersensitivity mechanism involved in the allergic response:

Immune system cell with antibodies

Immediate hypersensitivity or IgE mediated. When specific IgE immunoglobulins are involved in the immune response. They are usually reactions that appear quickly after contact with the allergen (less than an hour).


Delayed-type hypersensitivity. When the defences involved are the lymphocytes or white cells.

Substantiated information by:

Joan Bartra Tomàs
Rosa Maria Muñoz Cano

Published: 24 July 2019
Updated: 24 July 2019


Receive the latest updates related to this content.

Thank you for subscribing!

If this is the first time you subscribe you will receive a confirmation email, check your inbox

An error occurred and we were unable to send your data, please try again later.