What are allergies?
Your body's immune system normally protects the body against harmful substances such as bacteria and viruses. Allergy occurs when the immune system reacts to substances (called allergens) that are generally harmless and in most people do not cause an immune response. Individuals with allergies fall into two categories: those who can have life-threatening reactions when exposed (called anaphylaxis), and those who have symptoms that cause discomfort without being life-threatening
Allergies are relatively common. Both hereditary and environmental factors have been found to contribute to a predisposition to developing allergies. Allergies are described as seasonal (happening only at certain times of the year) or perennial (symptoms can occur year-round).
What happens during an allergic reaction?
The first exposure to the allergen causes a mild immune response that sensitizes your immune system to the substance. The second and subsequent exposure to the allergen usually results in symptoms. The type of symptom that develops depends on the specific allergen, the part of the body where exposure occurs, and the way the immune system reacts to the allergen.
When an allergen enters the body, it triggers antibody production; these antibodies bind to cells that contain histamine. Histamine (and other chemicals) are released by these cells when the antibodies are stimulated by allergens. This causes itching, swelling of affected tissues, mucus production, muscle spasms, hives, rashes, and other symptoms. Symptoms vary in severity from person to person.
Allergies vary according to the type of allergen and the part of the body in which the allergic reaction occurs. The part of the body contacted by the allergen will, in part, also affect symptoms. For example, allergens that are inhaled often cause nasal congestion, itchy nose/throat, mucus production, cough, or wheezing. Ingestion of a food allergen, in addition to the risk of causing a severe reaction, can cause nausea, vomiting, abdominal pain, cramping or diarrhea. Allergies to plants often cause skin rash. Drug allergies usually involve the whole body.
Allergic reactions also can be caused by insect bites, jewelry, cosmetics, and almost any substance that contacts the body. Some people have allergic-type reactions to hot or cold temperatures, sunlight, or other physical stimuli.
