Erythromycin is a bacteriostatic macrolide antibiotic, but may be bactericidal in high concentrations. Although the mechanism by which erythromycin acts in reducing inflammatory lesions of acne vulgaris is not fully elucidated, it is presumably due to its antibiotic action. It inhibits the growth of P. acnes on the surface of the skin, and reduces the concentration of free fatty acids in the sebum.

Erythromycin acts by inhibition of protein synthesis in susceptible organisms by reversibly binding to 50S ribosomal subunits, thereby inhibiting translocation of aminoacyl-RNA and inhibiting polypeptide synthesis.

Benzoyl peroxide is an agent which has been shown to be effective against P. acnes, an anaerobe found in sebaceous follicles and comedones. The antibacterial action of benzoyl peroxide is believed to be due to the release of active oxygen. Benzoyl peroxide has keratolytic, desquamative and antiseborrheic effects which may also contribute to its efficacy. Benzoyl peroxide has been shown to be absorbed by the skin where it is converted to benzoic acid. Approximately 5% of the metabolite is excreted unchanged in the urine.