Contact Allergy and Allergic Contact Dermatitis From Propylene Glycol and Related Glycols: Cosmetic Skin Sensitisers After All?

BACKGROUND: Propylene glycol (PG) is widely used in cosmetic and pharmaceutical products, yet data on the prevalence of contact allergy to PG and related glycols, and their potential cross-reactivity, remain limited. OBJECTIVES: To determine the prevalence of glycol contact allergy, describe clinical characteristics and assess potential cross-reactivity. METHODS: We retrospectively analysed 1979 patients patch tested at Antwerp University Hospital between January 2021 and December 2024 who were tested with at least one glycol. RESULTS: Fifty-five patients (2.79%) were allergic to PG. Detection rates for PG increased with concentration: 5% petrolatum (1.06%), 10% aqueous (0%), 20% aqueous (0.66%), 30% aqueous (2.19%) and 100% (7.82%, selectively tested). Pentylene glycol allergy was found in 6.74% (6/89) and caprylyl glycol in 0.77% (5% petrolatum) and 0.12% (1% petrolatum). Concomitant reactions to PG occurred in 4/6 pentylene glycol-allergic and 2/9 caprylyl glycol-allergic patients. PG-allergic patients were predominantly female (63.6%), with dermatitis mainly affecting the face and hands. Cosmetics (67.3%) were the most common exposure source, followed by topical pharmaceuticals (41.8%). CONCLUSIONS: Thirty percent aqueous PG appears more suitable for screening than lower concentrations, and 100% PG may improve detection in selected cases. Cross-reactivity seems limited and is most evident among structurally similar short-chain glycols.