Walter Liszewski, MD, and Kara Mudd, PA-C, highlight their lecture Patch Testing Demystified: Distinguishing Positives From False Positives and Ensuring Relevance at the 2nd Annual Elevate-Derm Alliance Summer Conference in Park City, Utah, at the Grand Hyatt Deer Valley.

In this video

In this interview with dermatology PA Buchi Nita, Liszewski and Mudd walk through the practical mechanics of patch testing. They favor comprehensive testing as "the gold standard" over the true test, noting the true test may miss around 50% of allergens versus 5–10% with an expanded panel like the North American Series or ACDS series. They review which medications to hold and for how long — traditional immunosuppressants like mycophenolate, azathioprine, and methotrexate one to two weeks out; no tanning to the back for three to four weeks; low-dose prednisone (20 mg or less) when patients truly need it; JAK inhibitors "quick on, quick off" a few days prior; and holding IL-4/IL-13 inhibitors when feasible. Antihistamines can continue since they treat type I, not the type IV hypersensitivity patch testing targets, and topical corticosteroids should stop about two weeks prior in the areas being patched.

On scheduling, both describe Monday–Wednesday–Friday (or Thursday) reads, with home patch removal an option for distant patients as long as the final in-person read happens. For the final visit, they group positives into categories — fragrance, preservative, rubber — review patients' actual products since "labels are not intuitive," and send everyone home with a written plan and handouts. They point to the ACDS-sponsored CAMP app, which flags unsafe ingredients and lists safe alternatives when patients scan labels. And on the controversial closer, Liszewski defends parabens as weak, generally clinically insignificant preservatives that "get a bad rap," warning that paraben-free products often substitute "far more toxic preservatives."

  • Choose comprehensive testing when you can — the true test may miss roughly 50% of allergens versus 5–10% with expanded panels like the North American Series or ACDS series.
  • Plan medication holds ahead of time: immunosuppressants one to two weeks out, no back tanning for three to four weeks, prednisone at 20 mg or less only if needed, JAK inhibitors a few days prior, and hold IL-4/IL-13 inhibitors when feasible.
  • Continue antihistamines (they target type I, not the type IV reaction being tested), and stop topical corticosteroids about two weeks prior in the patched areas.
  • The final in-person read is mandatory; home patch removal can reduce visits for distant patients, but low-volume patchers should keep the Wednesday read to interpret correctly.
  • Close the loop at the final visit — review the patient's own products, group allergens into categories, provide a written plan, and use tools like the ACDS CAMP app so patients can scan labels for safe alternatives.