Propylene Glycol.

Propylene glycol (PG), an emollient and emulsifier found in cosmetics, medications, and food, has been granted the dubious honor of being named the American Contact Dermatitis Society's Allergen of the Year for 2018. Allergic and irritant contact dermatitis and systemic cutaneous reactions to PG, which has become an increasingly common ingredient, have been documented. Propylene glycol is as contentious as it is ubiquitous because it acts as both a weak sensitizer and an irritant, confounding the results of positive patch tests. This report serves to increase awareness about PG sensitization and appropriate testing and evaluation of PG patch tests.