Diagnosing food allergies involves a detailed evaluation of a patient's history of symptoms and their association with the intake of a specific food type. Blood or skin prick tests or food elimination diets may also be used to narrow down the possible triggers of allergy.

Diagnosis outline

• A detailed examination of past food exposure and the appearance of symptoms is carried out. The person with the allergy or their parents in the case of children, are asked to maintain a diary recording the frequency, duration and severity of symptoms and the time they take to appear along with details of all foods consumed. Any family history of similar food allergies or other allergic conditions such as asthma or eczema are also noted. Information on whether a child was breast or bottle fed may also be obtained as breastfed children are usually at a lower risk of food allergies.
• In cases where the patient is a child, growth and development are assessed.
• A food elimination diet may be used to check whether a certain food item is causing the allergy and a diet that completely lacks the suspected food item is followed for two to six weeks, after which it is gradually reintroduced. If the symptoms reduce or disappear when the food is withdrawn, only to reappear when it is included again, the food allergy is confirmed. This method should be carried out under medical supervision to avoid medical emergencies such as anaphylaxis.
• For people with an IgE-mediated food allergy, a skin prick test is recommended. Drops of highly diluted food items are placed over the forearm and the skin pierced using a tiny needle to see whether an allergic response such as redness ensues. Again, adequate medical support should be available to accommodate for any medical emergencies.
• Blood tests to detect antibodies to specific antigens may also be performed.
• Food allergy is sometimes confused with food intolerances such as lactose or gluten intolerance which may cause abdominal pain, bloating or diarrhea.