Emollient ditrimethylolpropane tetracaprylate penetrates the stratum corneum and maintains hydration without disrupting lipid structure

Emollients are essential for skin hydration, yet the relationship between their penetration into the stratum corneum (SC) and moisturizing efficacy remains unclear. This study aimed to elucidate the mechanism of the ester oil, ditrimethylolpropane tetracaprylate (DTTC), focusing on its persistent hydration effect and its interaction with SC lipids. We compared DTTC with other emollients and an occlusive benchmark using in vivo assays, permeability studies, and differential scanning calorimetry (DSC). In vivo, DTTC produced a superior and sustained hydrating effect after wash-off, without disrupting barrier function. Permeability analyses confirmed that DTTC penetrates and is retained within SC, in contrast to less persistent or non-penetrating agents. Furthermore, DSC showed that DTTC integrates into a model SC lipid matrix with high compatibility and minimal structural disruption. We conclude that the superior performance of DTTC reflects a dual mechanism: effective penetration and retention within SC, together with structurally compatible integration into the intercellular lipid matrix. This highlights a pathway to long-lasting hydration beyond simple surface occlusion and provides a basis for the rational design of advanced emollients.