What are allergies?

Allergy, defined by the World Health Organization (WHO) as 'immunologically mediated hypersensitivity', is increasing and it is estimated that over 20% of the world's population suffers from IgE-mediated allergic diseases.

Allergy knows no boundaries and affects people of all age groups, from infancy to childhood, from adolescence to adulthood up to the elderly. The Allergic Patient in Europe.

Genetically predisposed people have an abnormal reaction to certain stimuli, which are usually harmless. When they come into contact with these stimuli their body reacts aggressively, as if the stimulus was potentially damaging, producing in many cases immunoglobulin (IgE) antibodies, and activating immune cells, such as eosinophils or mast cells. This usually occurs after repeated exposure. The initial process, by which an individual becomes sensitive, is called “allergic sensitisation”. The offending substances are called “allergens”. Clinical allergy symptoms are a consequence of the release of damaging substances from the activated cells. People who are constitutionally predisposed to produce IgE antibodies and have allergy symptoms are termed “atopic”.

The type of allergic reaction depends on the individual's immunological makeup and the organ affected by allergy, i.e., the "target organ”). So, allergic people may have allergic rhinitis and asthma (target organ: upper and lower airways), conjunctivitis (target organ: the eye), eczema, urticaria and angioedema (target organ: the skin), and food allergy (target organ: all the above, plus in some cases the gastrointestinal tract). Even if allergic symptoms appear in these target organs, allergy is a systemic disease in which the whole defence system of the body is involved, although symptoms may appear in only one target organ. These manifestations can appear singly or in various combinations in the same patient and at any time during life. If the whole body suddenly responds to the allergen, there will be an acute, generalized allergic reaction, which is called “anaphylactic” reaction.Anaphylactic reactions may result in the drop of blood pressure, in which case we have an anaphylactic shock, which can be very severe and may even be fatal.

In addition to allergens, irritants frequently cause symptoms in allergic individuals. However, some non-allergic people can also have hypersensitivity to irritants and substances. This is called intolerance and the symptoms are perceived by many patients as allergy. A correct diagnosis is needed to apply the adequate treatment and control.