Xylitol

Xylitol is a sugar alcohol used mainly as a humectant/skin-conditioning agent, typically at low-to-moderate percentages in leave-on products, and it is generally well tolerated in patch testing and routine cosmetic use. While not an acid or preservative and not inherently sensitizing, it can still cause occasional stinging or irritation on severely compromised skin (e.g., active eczema fissures) due to osmotic effects, so I rate it as very gentle rather than exceptionally gentle. Safety Notes: In commercial skincare, xylitol is often used at low levels (~0.05–0.5%) in leave-on moisturizers, serums, and barrier-support products as part of humectant blends or in combination with other polyols/sugars. Mid-range use (~1–5%) is common where it is positioned as a key humectant/osmoprotectant in lotions and creams. The highest consumer-available strengths are seen in specialized hydrating gels/creams and some sheet-mask/essence-type formulas, where xylitol can reach roughly 10–15% before tackiness, crystallization risk, and sensory constraints typically limit further increases; rinse-off products generally sit at the lower end due to brief contact time.