Nutritional Supplements and Cosmetic Formulations: A Review of Emerging Allergens.

Nutritional supplements and topical formulations are increasingly implicated in allergic contact dermatitis (ACD), yet their allergenic potential remains underrecognized due to inconsistent regulatory oversight, limited provider awareness, and the misconception that "natural" products are inherently safe. To identify emerging allergens in supplements and cosmetics, characterize associated ACD reactions, and highlight diagnostic and regulatory challenges. A systematic review of PubMed, Embase, MEDLINE, Web of Science, and CENTRAL databases was conducted to evaluate reports of ACD linked to dietary supplements and topical formulations. Key sensitizers include vitamin derivatives (tocopherol, phytonadione, ascorbic acid), herbal extracts (Ginkgo biloba, turmeric, St. John's Wort), and antioxidants (α-lipoic acid, resveratrol). Documented cases range from localized dermatitis to systemic reactions. Patch testing confirms sensitization, with cross-reactivity and oxidation-related allergenicity frequently observed. Patch testing may not always reveal the sensitizing agent, especially if the allergen is a contaminant, an unlisted ingredient, or undergoes chemical transformation during oxidation or formulation. The rising prevalence of supplement- and cosmetic-induced ACD underscores the need for standardized patch testing, improved ingredient labeling, and enhanced regulatory oversight, including mandated reporting of adverse reactions, premarket safety testing for allergens, and standardized labeling of known sensitizers and botanical components.