An allergy occurs when your immune system reacts to a foreign substance in the body. This could include something that you have eaten, something that has come into contact with your skin or something that you have inhaled. Allergies commonly affect both adults and children. According to the Centers for Disease Control and Prevention, 28.5 million children aged 5 to 11 were reported with common allergies in 2010. The symptoms of an allergy can vary significantly and can range from being very minor to potentially life-threatening.
Causes. Allergies occur when your immune system reacts to a substance that is normally harmless. The immune system produces antibodies, which, according to the Mayo Clinic, are then always on the lookout for a certain substance. If you are subsequently exposed to the substance, these antibodies release different chemicals, which cause the allergy symptoms. One such chemical is histamine, which causes the symptoms of hay fever, a common allergy.
Common triggers. While it is possible to be allergic to pretty much any substance, there are a number of common triggers that cause a reaction in many people. Airborne allergens like pollen, dust mites and animal dander (dead skin) often cause allergic rhinitis (or hay fever). Many people suffer allergic reactions to certain food items, including nuts, wheat, fish and milk. Insect stings can cause an allergic reaction, as well as certain medications, such as penicillin.
Symptoms. Different allergies cause different reactions, and so the symptoms can vary from one patient to another. A lot of different allergies cause a reaction in the skin, including itchiness, redness or hives (itchy, red welts that appear on the surface of the skin). Hay fever sufferers normally experience congestion, a runny nose and watery, swollen eyes. Food allergies, in addition to causing hives and skin rashes, can cause swelling of the lips, tongue or throat, as well as irritation in the digestive system.
Severe reactions. Some allergies can trigger a very severe reaction known as anaphylaxis (or anaphylactic shock). In these cases, your body's reaction to the allergy is so severe that you can go into shock, with potentially life-threatening symptoms. Patients suffering anaphylaxis can lose consciousness and/or have difficulty breathing due to severe swelling in the airways. According to the UCLA School of Medicine, anaphylaxis causes around 1,500 deaths a year in the United States.