CHOLESTERYL BUTYRATE.

Cholesteryl Butyrate effectively acts as a prodrug, releasing the short-chain fatty acid butyrate directly into the skin. This active component exhibits potent anti-inflammatory properties by inhibiting the adhesion of inflammatory cells like polymorphonuclear cells (PMNs) to endothelial cells, potentially modulating the MAPK signaling pathway. It also functions as a histone deacetylase (HDAC) inhibitor, particularly HDAC3, to reduce inflammation and suppress *Staphylococcus aureus*-aggravated IL-33 expression. Butyrate further activates skin-resident regulatory T cells, contributing to immune modulation. Crucially for skin health, it promotes barrier integrity by enhancing keratinocyte metabolism and differentiation, leading to increased synthesis of essential lipids such as cholesterol and specific ceramides (e.g., ester-linked omega-hydroxy ceramides). This action helps reduce transepidermal water loss (TEWL) and supports skin's natural defense against environmental aggressors, including UV radiation and microbial imbalances, partially via G protein-coupled receptor (GPCR) activation.