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Propylene glycol (PG) is a solvent, vehicle, and humectant being used increasingly in a wide array of personal care products, cosmetics, and topical medicaments. Propylene glycol is a recognized source of both allergic and irritant contact dermatitis.The aim of the study was to report incidence of positive patch tests to PG at Mayo Clinic.We retrospectively reviewed records of all patients patch tested to PG from January 1997 to December 2016.A total of 11,738 patients underwent patch testing to 5%, 10%, or 20% PG. Of these, 100 (0.85%) tested positive and 41 (0.35%) had irritant reactions. Patients also tested to a mean of 5.6 concomitant positive allergens. The positive reaction rates were 0%, 0.26%, and 1.86% for 5%, 10%, and 20% PG, respectively, increasing with each concentration increase. The irritant reaction rates were 0.95%, 0.24%, and 0.5% for 5%, 10%, and 20% PG, respectively.Propylene glycol is common in skin care products and is associated with both allergic and irritant patch test reactions. Increased concentrations were associated with increased reactions.