A food allergy is an adverse immune response to a food protein. Food allergy is distinct from other adverse responses to food, such as food intolerance, pharmacologic reactions, and toxin-mediated reactions.

The food protein triggering the allergic response is termed a food allergen. It is estimated that up to 12 million Americans have food allergies, and the prevalence is rising.

Food allergies cause roughly 30,000 emergency room visits and 100 to 200 deaths per year in the United States.

Treatment consists of avoidance diets, in which the allergic person avoids all forms of the food to which they are allergic. For people who are extremely sensitive, this may involve the total avoidance of any exposure with the allergen, including touching or inhaling the problematic food as well as touching any surfaces that may have come into contact with it. Areas of research include anti-IgE antibody (omalizumab, or Xolair) and specific oral tolerance induction (SOTI), which have shown some promise for treatment of certain food allergies. People diagnosed with a food allergy may carry an autoinjector of epinephrine such as an EpiPen or Twinject, wear some form of medical alert jewelry, or develop an emergency action plan, in accordance with their doctor.

Signs and symptoms

Classic immunoglobulin-E (IgE)-mediated food allergies are classified as type-I immediate hypersensitivity reactions. These allergic reactions have an acute onset (from seconds to one hour) and may include: "Food allergy"

• Angioedema: soft tissue swelling, usually involving the eyelids, face, lips, and tongue. Angioedema may result in severe swelling of the tongue as well as the larynx (voice box) and trachea, resulting in upper airway obstruction and difficulty breathing.
• Hives
• Itching of the mouth, throat, eyes, skin
• Nausea, vomiting, diarrhea, stomach cramps, and/or abdominal pain. This group of symptoms is termed gastrointestinal hypersensitivity or anaphylaxis.
• Rhinorrhea, nasal congestion
• Wheezing, scratchy throat, shortness of breath, or difficulty swallowing
• Anaphylaxis: a severe, whole-body allergic reaction that can result in death (see below)

The reaction may progress to anaphylactic shock: A systemic reaction involving several different bodily systems including hypotension (low blood pressure),loss of consciousness, and possibly death. Allergens most frequently associated with this type of reaction are peanuts, nuts, milk, egg, and seafood, though many food allergens have been reported as triggers for anaphylaxis.

Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma. The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.