The science
Salicylic acid is a lipophilic beta-hydroxy acid that penetrates the sebum-filled follicle, where it dissolves intercellular cement and loosens the corneocyte plugs that form comedones; at 2 percent it is the maximum concentration permitted for over-the-counter acne products under the FDA monograph, and controlled studies of 2 percent salicylic acid cleansers show measurable reductions in comedones and mild inflammatory lesions with twice-daily use, though effect sizes are smaller than for leave-on products because of short contact time. Glycolic acid at a declared 2.9 percent, partly neutralised by sodium hydroxide, adds alpha-hydroxy exfoliation of the surface, which in rinse-off use modestly improves texture and the turnover of post-inflammatory marks. Azelaic acid at a declared 1 percent is far below the 15 to 20 percent at which its anti-inflammatory, antibacterial and tyrosinase-inhibiting effects are documented in leave-on prescription products, and no evidence supports an effect at this level in a wash; its inclusion is nominal.
The surfactant system determines tolerance. Cocamidopropyl hydroxysultaine is an amphoteric surfactant with low irritation potential that boosts foam and mildness; disodium and sodium cocoyl glutamate are anionic amino-acid surfactants with among the lowest protein-denaturation and lipid-extraction scores in comparative studies. Together, and without sulfates, they cleanse at a pH compatible with the acids while preserving more barrier lipid than conventional acne washes, which is the mechanistic basis for the reduced post-wash tightness. Bentonite is an absorbent clay that binds sebum during cleansing and thickens the gel; niacinamide at the eighth position supports barrier lipid synthesis and reduces erythema, with rinse-off contact limiting but not eliminating its contribution. Green tea leaf extract adds polyphenol antioxidants, and the dextrin, polydextrose and amylopectin trio is a texturising starch complex. Preservation is a mild system of a radish-root ferment, ethylhexylglycerin, potassium sorbate and phenoxyethanol.
Tolerance considerations are the acid trio on dry, atopic, rosacea-prone or barrier-compromised skin; increased ultraviolet sensitivity from salicylic and glycolic acids warranting daily sunscreen; and the additive irritation of stacking leave-on acids. Salicylic acid in a 2 percent rinse-off is generally regarded as acceptable in pregnancy owing to minimal systemic absorption, though the brand makes no claim. The formula is fragrance-free, alcohol-free and free of comedogenic lipids. Skinfix reports dermatologist testing but publishes no clinical study.