Isoleucine

We confirmed this ingredient's definition and its registered function in public regulatory databases, but found no published study data on how the ingredient itself acts on the skin (checked by KAIAN, September 2026). We will update this page if new reports appear.

One of the branched-chain amino acids (BCAAs), formulated to condition the skin

Reported to be present in small amounts in an analysis of free amino acids in human stratum corneum and skin surface film (a 1966 study). Reports positioning it as a major NMF constituent, and human studies showing an effect of topical application alone, were not confirmed

No public data on typical concentrations in cosmetics could be confirmed (varies by product)

No public data on the time to a perceptible effect with topical use could be confirmed

Ingredient-specific irritation data not confirmed. The US CIR Expert Panel concluded that α-amino acids are safe as cosmetic ingredients under the practices of use and concentration assessed (2013; whether this ingredient was among those assessed is unconfirmed)