Cytokines from mast cells may also play a role in the persistence of long-term effects. Diagnosis
Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge. For skin-prick tests, a tiny board with protruding needles is used. The allergens are placed either on the board or directly on the skin. The board is then placed on the skin, to puncture the skin and for the allergens to enter the body. If a hive appears, the person is considered positive for the allergy. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin-prick tests.Skin-prick testing is easy to do and results are available in minutes. Different allergists may use different devices for testing. Some use a "bifurcated needle", which looks like a fork with two prongs. Others use a "multitest", which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular food or not because it detects IgE.
Typically, the sensitivity is to proteins in the white, rather than the yolk.Milk from cows, goats, or sheep is another common food allergen, and many affected people are also unable to tolerate dairy products such as cheese. A small portion of children with a milk allergy, roughly 10%, have a reaction to beef because it contains small amounts of protein that are also present in cows milk.Seafood is one of the most common sources of food allergens; people may be allergic to proteins found in fish or to different proteins found in shellfish (crustaceans and mollusks).Other foods containing allergenic proteins include soy and wheat, and to a lesser frequency, fruits, vegetables, maize, spices, synthetic and natural colors, and chemical additives.Balsam of Peru, which is in various foods, is in the "top five" allergens most commonly causing patch test reactions in people referred to dermatology clinics. Other than oral ingestion
Sensitization can occur through the gastrointestinal tract, respiratory tract and possibly the skin. Damage to the skin in conditions such as eczema has been proposed as a risk factor for sensitization.While the most obvious route for an allergic exposure is oral ingestion, some reactions are possible through external exposure. Peanut allergies are much more common in adults who had oozing and crusted skin rashes as infants. Airborne particles in a farm- or factory-scale peanut shelling or crushing environment, or from cooking, can produce respiratory effects in exposed allergic individuals.