What are they?
Allergies are hypersensitivities, overreactions of the immune system to substances that do not cause reactions in most people. Hypersensitivities are grouped into four types, I through IV. These classifications are based, to some extent, on what parts of the immune system are activated and how long it takes for a reaction to occur.
The two types of hypersensitivities commonly associated with the term “allergies” are type I immediate hypersensitivities, in which antigens (allergens, foreign substances) combine with specific IgE (immunoglobulin E) antibodies to cause local and sometimes systemic reactions – usually within minutes; and type IV delayed hypersensitivities, reactions caused by the interactions of antigens with specific sensitized T lymphocytes instead of antibodies.
Type I hypersensitivities affect mainly the respiratory and gastrointestinal systems and the skin. They occur most frequently in those with a predisposition to allergies (those whose parents have allergies are more likely to have them themselves, although not necessarily to the same substances). The first time a predisposed person is exposed to a potential allergen, they will not have a major reaction; instead, they will create a specific IgE antibody and become “sensitized.”
The IgE antibody produced then attaches itself to mast cells, specialized cells in the tissues, and basophils (a type of white blood cell) in the blood stream. This action primes the immune system. During subsequent exposures to the allergen, that specific bound IgE identifies the intruder, attaches to it, and triggers the release of chemicals, including histamine, causing allergic symptoms that start in the mouth, nose, or on the skin, wherever the allergen was introduced.
What is not an allergy?
There are other reactions that can cause allergy-like symptoms but are not caused by an activation of the immune system. They range from toxic reactions that affect anyone who has sufficient exposure, such as food poisoning caused by bacterial toxins, to genetic conditions, such as intolerances caused by the lack of an enzyme (for example, the inability to digest milk sugar, resulting in lactose intolerance) and sensitivities to things like gluten (in celiac disease). Symptoms can also be caused by medications such as aspirin and ampicillin, food dyes, MSG (monosodium glutamate – a food flavor additive), and by some psychological triggers. While these diseases and conditions may need to be investigated by your physician, they are not allergies and will not be identified during allergy testing.
Information taken from Labtestsonline
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