Definition of Allergy
An allergy is an abnormal and specific reaction of the body in contact with a foreign substance (allergen). Usually foreign substances do not cause trouble in most people but others are not so fortunate.
For an allergy to occur, it is necessary that an initial contact took place between the allergen and the body of the subject. That is why it is often the second contact to the allergen that is most problematic.
There are different forms of expressions of allergies or allergy:
- Asthma
- Atopic dermatitis, atopic eczema, eczema (in general)
- Hay fever (allergic rhinitis)
- Conjunctivitis
- Hives
- Allergies to medicines
- Food allergies (often it is in fact a pseudo-allergy = poor digestion)
How does an allergy take effesct?
When a person with a sensitive immune system is exposed to an allergen, a series of events occurs:
1. The body begins to produce antibodies ussually a specific type called immunoglobulin E (IgE), to fight against allergens (by various mechanisms such as neutralization).
2. Antibodies attached to the antigen bind to cells called mast cells. Mast cells are found in large numbers in the airways and the gastrointestinal tract, where allergens are trying to enter the body.
3. This then produces the release of molecules contained in the mast cells and these are responsible for most of the symptoms of allergy sufferers such as a stuffy nose or red eyes.
If the allergen is in the air, the allergic reaction takes place in the eyes, nose or lungs. If the allergen is ingested, the allergic reaction happens in the mouth or gastrointestinal tract. Similarly when the allergen is in contact with skin, this will produce dermatological reactions (eg eczema).
However allergic reactions can sometimes go beyond the classic allergic reaction, and this is called a generalized allergy, this can result in a drop in blood pressure and even loss of consciousness. This type of severe allergy is called anaphylaxis and often requires emergency treatment for life (eg for people with severe allergies to bee stings, they should always carry with them an adrenaline-based injection).
3. Statistics on the frequency of allergy sufferers say that that two out of ten Americans are affected by allergies, these figures are probably similar in Europe because the Americans are mostly “old” Europeans.
Most allergies are inherited, which means they are transmitted from parents to children. For example when a parent is allergic, their child has a 50% of being allergic as well. When 2 parents are both allergic, this probability can go up to 75%. Note that children inherit a tendency to be allergic, but not necessarily to the same allergen.