An allergy refers to an exaggerated reaction by our immune system in response to exposure to certain foreign substances. The response is exaggerated because these foreign substances are usually seen by the body as harmless and nonallergic individuals do not produce a response. In allergic individuals, the body recognizes the foreign substance, and one arm of the immune system generates a response.
Allergy-producing substances are called "allergens." Examples of allergens include pollens, dust mites, molds, animal proteins, foods, and even medications. To understand the language of allergy, it is important to remember that allergens are substances that are foreign to the body and can cause an allergic reaction in certain people. When an allergic individual comes in contact with an allergen, the immune system mounts a response through the IgE antibody. Therefore, people who are prone to allergies are said to be allergic or "atopic."
Allergies can develop at any age, and the initial exposure or sensitization period may even begin in while the fetus is in the uterus. Individuals can also outgrow allergies over time. Whereas many children outgrow food allergies, nasal or environmental allergies often develop over time.
Why, you may ask, are some people "sensitive" to certain allergens while most are not? Why do allergic people produce more IgE than those who are nonallergic? Although we certainly do not fully understand why one person develops allergies and another does not, we know there are several risk factors for allergic conditions. Family history, or genetics, plays a large role, with a higher risk for allergies if parents or siblings have allergies. There are numerous other risk factors for developing allergic conditions. Children born via Cesarean section have a higher risk of allergy as compared to children who are delivered vaginally. Exposure to tobacco smoke increases the risk of allergy. Boys are more likely to be allergic than girls. Exposures to antigens, use of antibiotics, and numerous other factors, some of which are not yet known, also contribute to the development of allergies.