What Is an Allergy?
Allergy is when a person's immune system reacts to a substance it has become sensitized to.
There is a lot in that short definition, so let's walk through it.
Antagonists and the immune system
The immune system is a complex network of cells and proteins that defends the body against antagonists. These antagonists can be bacteria, viruses, parasites, toxins, or even foreign particles such as a wood splinter.
The similarity between these antagonists is that they can cause damage to the body. In response, the immune system has evolved to employ specific defenses against different threats. In the context of allergy, the important defense to know is the antibody immunoglobulin E (IgE), which is the driver of most allergic reactions.
Sensitization and allergy
Allergens, which can include various things such as food, pollen, bee venom, or pet dander, are substances that the immune system can become sensitized against and react to. Sensitization is when the immune system registers a substance as a threat and produces antibodies against it. Allergy is the resulting reaction once these antibodies are utilized.
These antibodies attach to various immune cells in the body. When the allergen is encountered, these cells can release inflammatory mediators such as histamine, which leads to an allergic reaction. If enough of these cells are triggered, anaphylaxis, a severe allergic reaction, can occur.