Allergies: Medically Explained

Allergies are the immune system's abnormal way of reacting to foreign substances. It is a local or systemic inflammatory response to allergens, or substances that cause allergic reactions. When exposed to allergens, the immune system produces Immunoglobulin E (IgE) to protect the body. These IgE antibodies cause certain cells in the body to release chemicals such as histamine, which affects a person's eyes, nose, throat, lungs, skin, or gastrointestinal tract in such a way that allergic reactions occur. Continued exposure to these allergens induces the same antibody reaction.

An allergic reaction, or a hypersensitive response, is the result of how allergens, mast cells, and Immunoglobulin E (IgE) interact with the body. Allergens include pollen, dust mites, certain foods, animal dander, insect bites and stings, airborne particles, latex, medicines and certain chemicals. Mast cells mostly reside in connective tissues in the skin, tongue, nose, intestinal tract, lungs and upper airways. IgE, which coats the surface of the mast cells in tissues, is an allergic antibody. It is a type of protein produced by the immune system to recognize and fight foreign substances that invade the body.

When an allergy-prone person is exposed to an allergen, large amounts of IgE antibodies are produced. These cause the mast cells to discharge inflammatory chemicals that cause tissues to swell, histamine and others that cause itching, bingeing of blood vessels, increased secretions, and bronchospasm, a spasm associated with asthma and bronchitis that makes exhalation difficult and noisy. Some of the chemicals attract white blood cells called eosinophils, which increase inflammatory chemicals.

Allergic reactions can be mild or severe (anaphylactic). Mild reactions include local symptoms, meaning only a specific area of the body is affected. Symptoms include swelling of the nasal mucosa (allergic rhinitis); redness and itching of the conjunctiva (allergic conjunctivitis); bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma; feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage; various rashes like eczema, hives or contact dermatitis; and headaches, which are observed in some with environmental or chemical allergies. Anaphylaxis, or systemic allergic response, is a life-threatening severe reaction characterized as sudden and systemic (affecting the whole body). It may start with itching of the eyes or face and develop into more serious symptoms in minutes. It could lead to swelling, difficulty in breathing or swallowing, abdominal pain, vomiting, diarrhea and hives. Since anaphylaxis causes the blood pressure to quickly drop, mental confusion or dizziness may occur. Depending of the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma and even death.

Allergies are mostly inherited. But a person doesn't usually inherit the same allergy, just the likelihood of having allergies. Allergies may also develop during exposure to allergens when the body's defenses are down, such as after a viral infection or during pregnancy.

Although people with colds and allergies display similar symptoms, there are ways to distinguish the two. Colds can occur at any time, worsen as the days go by, and then gradually get better. Colds may also be accompanied by fever, aches and pains. Allergies, on the other hand, begin immediately after being exposed to an allergen and last as long as exposure to the offending substance continues.