By Maureen Egan, MD
While there is much we don’t know about how patients become sensitized to food allergens, there is no current evidence that skin prick testing (SPT) in any way contributes to a patient developing a food allergy (or other allergies). Skin testing is based on the presence of the allergic antibody (IgE) to a given substance. The introduction of the extract (i.e. allergen you are testing for) into the top layer of the skin binds to IgE only if an individual already has it present, the skin test itself can not produce IgE. This technique has been in use since 1924. While the incidence of food allergies has increased dramatically in the past couple of decades, the long history of safe use of SPT is persuasive evidence that they are not correlated.
Research from the United Kingdom shows that allergic antibodies to peanut may be triggered through chronic skin exposure of peanut protein found in house dust. This has raised fears that SPTs might also be an induction point for food allergies. Much of the current evidence on cutaneous sensitization (development of allergic antibody through skin exposure) focuses on chronic exposure in patients with skin barrier dysfunction, such as eczema. The chronic exposure to an infant’s eczema, which opens deeper layers of the skin, to a durably bio-active allergen is far different from a single superficial exposure with a small amount of allergen. Additionally, skin testing is not performed in the areas of active skin inflammation.
While there was a recent case report published describing a female who likely developed an oat allergy from skin exposure through oatmeal in skin products, it should be highlighted that this patient had significant atopic dermatitis that was resistant to mainstay medical treatments and used the oatmeal containing product chronically on an impaired skin barrier. Additionally, the widely publicized LEAP trial performed skin testing on high-risk infants and subsequently completed oral challenges and found a strong correlation between skin test results and clinical reactions (i.e. patients with negative skin tests were able to eat the food) indicating that the skin testing itself was unlikely to play a role in the development of an allergy.
The natural history of food allergy similarly argues against skin testing being a contributor to disease. The most common food allergies are milk and egg which are typically diagnosed based on a clinical reaction and thus before a child is even referred to an allergist and has skin testing performed. Additionally, milk and egg allergy are typically outgrown which would not be the case if skin testing were repeatedly sensitizing them.
Maureen Egan, MD is currently a clinical fellow in Allergy and Immunology at the Icahn School of Medicine at Mount Sinai in New York. She is a graduate of Georgetown, completed medical school at Loyola University Chicago-Stritch School of Medicine the Pediatric Residency program at New York University where she was Chief Resident for the NYU Pediatric Residency program for 2013-2014 and did a rotation at the practice of Dr. Paul Ehrlich. For more on Dr. Egan, click here.