Sulfamethoxazole (SMX) is an antibiotic in the Sulfonamide family. It is used to treat certain types of respiratory tract, urinary tract and skin infections that are caused by bacteria. Sulfamethoxazole is rarely used alone. It is primarily available in combination with another antibiotic called Trimethoprim. This combination is called Co-Trimoxazole, and it is a very common antibiotic.

Sulfamethoxazole is rarely used by itself as a treatment for acne. However, Co-Trimoxazole is a popular treatment for moderate to severe acne symptoms. Both clinical research and laboratory testing indicates that Co-Trimoxazole can be an excellent acne treatment, particularly for individuals with inflammatory acne symptoms.

Laboratory testing has indicated that the acne-causing P. acnes bacteria is moderately susceptible to Sulfamethoxazole. P. acnes bacteria are also moderately susceptible to Trimethoprim. These two antibiotics are synergistic, and the combination is substantially more toxic to P. acnes bacteria.