Lactic AcidvsSulfur

Lactic acid (90 Da, larger than glycolic acid) exfoliates via the standard AHA mechanism: chelating calcium at corneodesmosomes and promoting desquamation through protease activation. Unlike glycolic acid, lactic acid is a natural component of the skin's natural moisturizing factor (NMF) and functions as a humectant, drawing water into the stratum corneum through hygroscopic binding. It inhibits tyrosinase enzyme activity in melanocytes, providing mild brightening. At higher concentrations (10%+), lactic acid upregulates serine palmitoyltransferase and glucosylceramide synthase in keratinocytes, stimulating ceramide synthesis and improving barrier lipid composition. It also enhances filaggrin proteolysis to NMF components. This dual action—exfoliation plus barrier support—makes it the most moisturizing AHA and clinically useful for dry, sensitive, or barrier-compromised skin.

Elemental sulfur (S8) reacts with cysteine residues in stratum corneum proteins to form hydrogen sulfide (H2S) and thiol derivatives, reducing disulfide bonds in keratin K1/K10 and cornified envelope — loosening corneocyte cohesion and promoting desquamation. Breaks hyperkeratotic plug in follicular ostia, unclogging pores. Bacteriostatic against Cutibacterium acnes through metabolism and membrane disruption. Reduces sebum production, possibly via anti-androgenic effects on sebaceous glands. Antifungal against Malassezia furfur (seborrheic dermatitis, pityrosporum folliculitis) via ergosterol synthesis inhibition. Anti-inflammatory effects may involve H2S signaling — endogenous H2S has vasodilatory properties. Mild comedolytic. Well-tolerated: works primarily on stratum corneum without deep penetration.