Propylene Glycol

Propylene glycol is a common humectant/solvent typically used around ~1–10% (sometimes higher) and is generally well tolerated, but it is also a recognized irritant for a meaningful minority of users, especially on compromised skin or at higher concentrations/occlusion. Patch testing and clinical experience show it can trigger irritant dermatitis and occasionally contact allergy in sensitive populations (including eczema patients), so I rate it as mild rather than “gentle” for patient-safety. Safety Notes: In commercial skincare, propylene glycol is often used at very low levels (~0.1–1%) as a solvent/humectant or to aid preservation and fragrance/actives solubilization, including in both leave-on lotions/serums and rinse-off cleansers. Typical mainstream leave-on products commonly sit around 2–15%, while higher levels are seen in fast-drying hydroalcoholic gels, makeup/skin prep products, and some OTC antifungal/medicated-style creams where propylene glycol functions as a solvent and penetration enhancer. Consumer-available extremes reach roughly 40–60% in certain specialty gels/solutions (still OTC), whereas concentrations above this are uncommon in skincare due to tack/irritation and sensorial limits; no specific EU/FDA maximum is set for propylene glycol in cosmetics, but practical tolerability drives the upper end.