Ever wonder if an allergy might be the root cause of your skin condition, or a trigger for your flare-ups? Allergy testing can sometimes be helpful to zero in on foods and environmental culprits that may be contributing to a skin condition. But they aren’t always accurate, and the type of testing you do matters. Furthermore, there are specific reasons why they may not be a reliable diagnostic tool for patients with eczema or TSW.
Allergy Tests: What’s Reliable
Skin prick, skin patch, and blood tests in an allergist’s office are highly accurate for most people. They work by noting real-time inflammation after allergen exposure, or by measuring IgE, an antibody triggered by substances you are allergic or sensitive to.
The skin prick system, considered the most accurate, introduces a small amount of a suspected allergen into the skin. Then, the doctor waits and sees whether a mosquito-bite-like bump grows at the site of the prick. It takes about 20 minutes for the skin to react if an allergy or sensitivity is present.
Often, to save time, an allergist will map out a numbered grid on your arm or back, so that they can test several substances at once. Whichever number on the grid shows a raised red bump will indicate an allergic or sensitive reaction. The allergist will also examine the intensity of the reaction and give it a score, so that you can find out which substances you are the most reactive to.
The patch test works in a similar way. The allergist will place several numbered adhesive patches infused with suspected allergens to your skin (usually on your back) for 48 – 90 hours. When the patches are removed, the allergist will examine your skin for reactions.
Another less common variation of testing is an intradermal test, where a small amount of allergen will be injected just beneath the surface of your skin to see whether it triggers a reaction. It functions on the same system as a skin prick or skin patch.
The trouble with the tests above is that they may be too irritating and cause problems for those with an existing skin condition. If you have skin issues, it may be wise to ask your allergist for an IgE blood test. In this case, they will take a small blood sample from your arm and submit it to a lab to test for IgE reactions to suspected allergens. You won’t know the results for a few days, but your skin won’t be affected by the blood draw.
False-Positives Can be High for Those with Eczema and TSW
The one factor to be aware of when receiving in-office allergy testing from an allergist is that all of the above tests can present “false-positives” even under the best of circumstances — meaning they could indicate an allergy where there is none.
Since the tests are measuring levels of IgE, dermatologists often find that testing people with eczema and TSW presents an even higher percentage of false-positives. Why? Because eczema and TSW patients often have higher levels of IgE in their blood to begin with. This skews the measurements, making solid allergy diagnoses difficult.
Another problem with false-positives on a food allergy test, is that the foods scoring high IgE reactions could actually ben non-allergenic and fine to eat for that eczema or TSW patient. Nonetheless, the patient might exclude all of the false positive foods in their quest to get better, compromising their nutrition and suffering through a restricted diet for no reason — and seeing no result in a reduction of skin symptoms.
What’s Never Reliable
Unfortunately, the much advertised at-home or mail-in tests that measure IgG antibodies are less reliable than IgE tests. Such mail-order tests often send back “food panels” that aren’t always accurate. Another concern is that at-home tests aren’t regulated by the FDA the way that doctors’ tests are.
Also, any allergy test needs to be accompanied by expert interpretation from a trained medical professional.
Conclusion
Making an appointment with an allergist could help you identify allergens that are impacting your health. If you have a skin condition, make a point of explaining the condition and your symptoms to your allergist. This will alert them to risks of skin irritation from patch or skin prick testing, and may prompt them to consider the possibility that your test might produce a higher percentage of false-positive results.
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About the Author
Olivia Hsu Friedman, LAc, Dipl.OM, DACM, Cert. TCMDerm, is the owner of Amethyst Holistic Skin Solutions and treats Acne, Eczema, Psoriasis, and TSW. Dr. Olivia treats patients via video conferencing using only herbal medicine. Dr. Olivia is past chair of the board of directors of the American Society of Acupuncturists, serves on the Advisory Board of LearnSkin, and is a faculty member of the Chicago Integrative Eczema Group sponsored by the National Eczema Association.