Currently, there is no single test to diagnose atopic dermatitis. However, there are some tests that can give the doctor an indication of allergic sensitivity.

Pricking the skin with a needle that contains a small amount of a suspected allergen may be helpful in identifying factors that trigger flares of atopic dermatitis. Negative results on skin tests may help rule out the possibility that certain substances cause skin inflammation. Positive skin prick test results are difficult to interpret in people with atopic dermatitis because the skin is very sensitive to many substances, and there can be many positive test sites that are not meaningful to a person's disease at the time. Positive results simply indicate that the individual has IgE (allergic) antibodies to the substance tested. IgE (immunoglobulin E) controls the immune system's allergic response and is often high in atopic dermatitis.

Recently, it was shown that if the quantity of IgE antibodies to a food in the blood is above a certain level, it is diagnostic of a food allergy. If the level of IgE to a specific food does not exceed the level needed for diagnosis but a food allergy is suspected, a person might be asked to record everything eaten and note any reactions. Physician-supervised food challenges (that is, the introduction of a food) following a period of food elimination may be necessary to determine if symptomatic food allergy is present. Identifying the food allergen may be difficult when a person is also being exposed to other possible allergens at the same time or symptoms may be triggered by other factors, such as infection, heat, and humidity.