1,2-Hexanediol

1,2-Hexanediol is a humectant/solvent and preservative booster typically used around ~0.5–2%, and it is generally well tolerated but not fully inert. Patch testing and real‑world reports show occasional irritation/stinging—especially on compromised barriers (eczema, post‑procedure) or when paired with other preservatives/actives—so I score it as mild to reflect a small but meaningful risk in highly reactive patients. Safety Notes: In commercial skincare, 1,2-hexanediol is most often used as a multifunctional humectant/solvent and preservative booster, commonly appearing around ~0.3–1.0% in leave-on serums/creams and rinse-off cleansers, with low-end usage observed around ~0.1% when it is a minor co-solvent within broader preservative blends. High-strength consumer-available formulations (especially “preservative-free” systems relying on glycols/diols for antimicrobial support, some minimalist K-beauty/toner/essence bases, and certain anhydrous or water-light formulas) can push total 1,2-hexanediol to about 3–5% for solubilization and preservation support, above which irritation/tack and sensorial limits typically constrain use in mainstream OTC products. It is not specifically concentration-restricted as a preservative in EU/FDA cosmetics, so the upper bound is primarily set by tolerability and formulation performance rather than a hard regulatory cap.