Allergy is a hypersensitive reaction of the immune system to normally harmless substances called allergens. Allergic reactions are caused by over-activation of certain while blood cells by an antibody called IgE, often involving rapid and severe inflammation. Reactions include anaphylaxis (a life-threatening, multi-symptom reaction), asthma attacks, hives, itching, pain, and vomiting. Treatments include desensitizing immunotherapy, antihistamines, and steroids.
Allergies often result from ambient allergens, airborne particles like dust or pollen. Reactions to these allergens take place in the parts of the body that are directly exposed, like the eyes (redness and itching), nose (sneezing, swelling of mucus membranes, stuffiness), throat (coughing), and lungs (asthma).
Food allergy is an immune response to food protein, not to include other reactions to food, like food intolerance and poisoning. Food proteins, or fragments of proteins, that are resistant to digestion are tagged as harmful with IgE, causing an immune system reaction. This reaction may be relatively mild, like eczema, more severe like hives, or life-threatening, like anaphylactic shock.
One of the most common food allergies is to peanuts. Peanut allergies may be particularly severe, triggered by tiny traces of peanut proteins causing extremely dangerous reactions. Peanut allergies are often outgrown.
Tree nuts, seeds, and their oils also contain proteins that may cause allergic reactions. Eggs and dairy products may also be allergens, although lactose intolerance is not an allergic reaction.
Non-food proteins, like latex and poison ivy, can also cause allergic reactions similar to those caused by food proteins, but they more commonly cause allergic contact dermatitis.