Patch Test (medicine) - Food Allergy

Food Allergy

There is often an assumption that certain foods can cause or worsen skin complaints like eczema. However, there is very little evidence that cutting out foods such as milk and eggs actually improves eczema.

Dermatologists may refer patients with suspected food allergies for patch testing. Sometimes this is justified as certain food additives and flavorings can cause dermatitis around the mouth, around the anus and vagina as food allergens pass out of the body or cause a widespread rash on the skin. While this is controversial, allergens such as nickel, Balsam of Peru, parabens, sodium benzoate or cinnamic aldehyde may worsen or cause skin rashes.

However, the foods that cause urticaria (hives) or anaphylaxis (such as peanuts) cause a type I hypersensitivity reaction whereby the part of the food molecule is directly recognized by cells close to the skin called mast cells. Mast cells have antibodies on their surface called immunoglobulin E (IgE). These act as receptors and if they recognize the allergen, they release their contents, causing an immediate allergic reaction. Type I reactions like anaphylaxis are immediate and do not take 2 to 4 days to appear. In a recent study of patients with chronic hives who were patch tested, those who were found allergic and avoided all contact with their allergen, including dietary intake, stopped having hives. Those who started eating their allergen again had recurrence of their hives. Often, patch testing for food allergies is not necessary, but in selected individuals it may be helpful.