That same biological mechanism used to defend the human body from unwanted viruses and bacteria is also the source of allergic reactions to everything from pollen to peanuts. The connection between allergies and the immune system involves a complex set of metabolic functions, which occur when the human body identifies harmless materials in the environment as a threat. Allergic reactions can be expressed by the body in different ways.
The human body produces allergens in response to foreign material that it considers to be a hazard. Once an undesirable substance enters the body and sets off an immune response, the body will continue to recognize it again and again when exposed. The reasons why this happens vary. In some cases, the body may be weakened from defending itself against a major illness and thus be more susceptible to developing an allergy.
A healthy immune system is capable of fighting the causes of disease, such as bacteria or viruses. It is also able to identify and get rid of human cells that have been damaged by disease. Sometimes, however, the human body overreacts, and its immune system cannot distinguish the difference between deadly and harmless substances. For example, this can happen from repeated exposure to objects like pollen, dust, mold, cat fur and peanuts.
The combination of allergies and the immune system response can result in an array of different kinds of allergic reactions, but many are not serious. One of the most common is nasal allergies, which can result from exposure to ragweed, grass or trees. The body can react to allergens in other ways too. Hives or a rash may develop from an allergy to substances, such as penicillin, or even foods like peanuts. In severe cases the body may go into anaphylactic shock, a deadly condition in which the blood pressure drops and breathing becomes difficult.
Treatments to relieve allergies and the immune system over-reaction resulting from exposure include over-the-counter medications and avoidance of allergen causing substances. Sometimes avoidance of these substances is not possible though. For this reason, a doctor may recommend immunotherapy or allergy shots.
New research to combat allergies and the immune system response to allergens is always being conducted. In an effort to treat common and potentially life-threatening allergies to peanuts, researchers performed an experiment in 2011 with mice that were sensitive to peanuts. The researchers introduced protein from peanuts to leukocytes, the white blood cells that ward off disease. Afterward, when the mice were exposed to eating peanuts they were no longer allergic, because the leukocytes ceased to recognize peanuts as being harmful.