10-Hydroxydecanoic Acid

10-Hydroxydecanoic acid is a medium-chain hydroxy fatty acid used as an antimicrobial/sebum-modulating component (notably in royal jelly derivatives) and is typically present at low levels, but as a free acid it can still sting or provoke erythema in compromised or highly reactive skin. Human irritation/sensitization data are limited compared with common fatty acids, so I do not treat it as inherently “gentle,” especially given its association with royal jelly–related allergenicity in some individuals. In real-world routines (often combined with other actives/preservatives), a mild irritation risk is plausible, warranting a cautious “mild” score. Safety Notes: 10-Hydroxydecanoic acid (a royal jelly–associated hydroxy fatty acid) is typically used in consumer skincare as a minor active within “royal jelly/10-HDA” complexes, where finished-product levels can be as low as ~0.001–0.01% in lotions/creams/serums that rely on extracts or blends. High-strength OTC products marketed around “10-HDA” (typically leave-on serums/spot products) are observed up to about 1% before sensory issues (waxy/soapy feel), solubility and pH-dependent salt formation, and irritation risk usually constrain further increases; rinse-off formats generally sit toward the lower end due to short contact time.