Carnitine

Carnitine (L-carnitine) is a water-soluble conditioning/sebum-modulating ingredient typically used at low concentrations (~0.1–2%) and is not inherently caustic or pH-dependent like acids. Human irritation and sensitization reports are uncommon in cosmetic use, but as a biologically active zwitterionic amino-acid derivative, it can occasionally sting on compromised barriers (eczema/post-procedure) when layered with other actives. Given sensitive-skin safety priorities, I rate it very gentle rather than exceptionally gentle. Safety Notes: In commercial cosmetics, carnitine (often listed as Carnitine or L-Carnitine) is most commonly used as a sebum-modulating/“oil control” and skin-conditioning active in leave-on serums, toners, and moisturizers, where low-end usage appears around 0.01–0.1% as a minor supportive active. Mainstream leave-on oil-control products frequently sit around ~0.5–2%, while the upper end observed in consumer-available “high strength” anti-oil/anti-blemish formulations reaches about 3% (higher levels are uncommon due to formula feel, solubility/ionic strength, and diminishing practical benefit). Rinse-off products typically use it at the lower end of the range because of brief contact time, whereas the highest levels are primarily seen in leave-on products.