Sarcosine

Sarcosine (N-methylglycine) is a small amino-acid derivative used in cosmetics mainly for sebum control and as a mild conditioning/humectant component, typically at low percentages. Available safety/patch-test experience suggests it is generally well tolerated and not a common irritant or sensitizer at typical leave-on levels, but any bioactive sebum-regulating ingredient can sting or provoke dryness in highly reactive or barrier-impaired skin when layered with other actives. To protect eczema-prone patients while staying consistent with clinical tolerability, I score it as very gentle rather than inert. Safety Notes: In commercial consumer skincare, sarcosine is most often used as a sebum-regulating/amino-acid active in leave-on products (serums, moisturizers, acne/oil-control treatments), where low-end usage is commonly around 0.05–0.2% as a supportive ingredient in multi-active formulas. Higher-strength consumer-available targeted oil-control/blemish formulations and some concentrated serum formats reach ~1–3%, with 3% representing the upper end seen in OTC retail products before sensory/stability constraints and diminishing returns typically limit further increases; rinse-off cleansers generally sit toward the low end due to short contact time.