Folic Acid

Folic acid (vitamin B9) is typically used in leave-on skincare at low concentrations for antioxidant/skin-conditioning support and is not an exfoliating, pH-dependent, or barrier-disrupting active. Clinical irritation and patch-test reports are uncommon, though rare hypersensitivity/contact dermatitis has been documented, so it cannot be considered fully inert. Given sensitive-skin safety priorities, it fits best as very gentle with low but nonzero irritation potential. Safety Notes: In commercial skincare, folic acid is most often used as a low-level skin-conditioning/antioxidant vitamin in leave-on serums and creams, with many products effectively dosing it in the ~0.0001–0.01% range (often as part of broader “B-vitamin” complexes). High-strength OTC specialty serums and ampoule-style products have been marketed up to about 0.1–0.5%, with the upper end constrained by solubility and stability (pH/light sensitivity) rather than regulatory caps; rinse-off products, when they include it, typically sit at the low end due to short contact time.