Creatine

Creatine is a skin-conditioning/osmolyte-type ingredient used in leave-on products typically around ~0.1–2%, where it is generally well tolerated and not inherently reactive. Available human data and real-world use suggest low irritancy, with occasional stinging possible mainly when applied to compromised barriers or when paired with other irritants in a routine. Given sensitive/eczema-prone populations and the need to avoid underestimating risk, it fits best as very gentle rather than inert. Safety Notes: In mass-market leave-on face creams/serums and anti-aging or anti-fatigue products, creatine is often used at very low “support” levels around 0.01–0.1% (frequently within broader energy/ATP-support complexes). In higher-performance OTC products (notably some anti-wrinkle eye/face treatments and hair/scalp strengthening leave-ons), creatine is commonly formulated around ~0.5–2%, with the upper end of consumer-available specialty formulations reaching about 5% before solubility/stability and sensorial constraints become limiting. Rinse-off products tend to use similar or lower levels than leave-on due to short contact time, with most of the high end observed in leave-on formats.