Salicylic Acid

A 1992 literature review in the journal Clinical Therapeutics looked four studies and one assay that assessed the effectiveness of 0.5-2% salicylic acid solutions in treating acne. In the studies reviewed, salicylic acid reduced the number and severity of acne lesions. The authors stated, "A review of four clinical studies and a comedolytic assay attests to the efficacy and safety of 0.5% and 2% solutions of salicylic acid for the treatment of acne vulgaris. In three placebo-controlled studies and a comedolytic assay, salicylic acid pads reduced the number of primary lesions and thereby the number and severity of all lesions associated with acne."⁵

A more recent 1996 study in the Journal of Dermatological Treatment investigated the effectiveness of a 2% salicylic acid lotion in treating mild to moderate acne. The researchers divided 114 university students into two groups: one group received salicylic acid lotion; the other group received a placebo (inactive substance). This study found that the group receiving salicylic acid experienced a greater reduction in acne lesions than the placebo group, especially after 8 and 12 weeks of treatment. Interestingly, salicylic acid reduced papules but not pustules in this study.⁶This is counterintuitive, because papules usually become pustules. The authors did not give a proposed reason for this outcome; one possible explanation is that the salicylic acid prevented papules from becoming pustules, but further research is necessary to explain this outcome.

A 2011 study in the Journal of the European Academy of Dermatology and Venereology compared the effectiveness of a combination tretinoin/clindamycin lotion and a combination salicylic acid/clindamycin lotion. This study found that both treatments resulted in a significant reduction in both inflammatory and non-inflammatory lesions. The group of patients receiving the tretinoin/clindamycin combination showed improvement sooner than the salicylic acid/clindamycin group, but by the 12-week mark, there was no significant difference between the two groups.³Researchers generally consider topical retinoids such as tretinoin to be more potent than salicylic acid, though salicylic acid typically has fewer side effects than tretinoin and is sometimes prescribed instead of tretinoin for this reason. This study, however, suggests that while tretinoin in combination with clindamycin may produce faster results, salicylic acid in combination with clindamycin eventually has a comparable outcome.

A 2012 study in The Journal of Dermatology explored whether adding salicylic acid to a clindamycin/benzoyl peroxide combination solution increased the effectiveness of the solution. In this study, researchers divided 50 patients with mild to moderate acne into two groups: one group received only clindamycin/benzoyl peroxide plus a placebo; the other group received clindamycin/benzoyl peroxide plus salicylic acid. This study found that the group receiving salicylic acid plus clindamycin/benzoyl peroxide experienced significantly more improvement in both non-inflammatory and inflammatory acne lesions than the group receiving only clindamycin/benzoyl peroxide. The authors speculated that the improvement experienced by the group receiving salicylic acid plus clindamycin/benzoyl peroxide might be due to the fact that salicylic acid helps clear pores of dead skin and sebum, thus allowing better penetration of the other medications.⁷

A 2013 study in the journal Skin Research and Technology tested the effectiveness of a 1.5% salicylic acid cream containing natural skin penetration enhancers (natural ingredients that help other ingredients penetrate into the skin). This study had two parts: (1) testing the effectiveness of the penetration enhancer in the lab; and (2) testing the combination salicylic acid plus penetration enhancer cream in patients. In the first part of the experiment, the researchers found that penetration into the skin of the combination product was twice that of salicylic acid without the penetration-enhancing cream. In the second part of the experiment, 20 patients with facial acne received this combination cream twice daily for four weeks. Results showed that 95% of patients experienced at least some improvement in their acne, and 20% experienced complete clearing of their acne. The researchers also found that both inflammatory and non-inflammatory lesions decreased during the four weeks of treatment.⁸This study needs to be interpreted with caution, however, for several reasons: some of the ingredients in the penetration enhancer product are already known to help reduce acne, so improvement might have been due to these ingredients rather than to the salicylic acid; the penetration enhancer was tested on pig skin, and thus we cannot assume that human skin would react the same way; and the authors of the study omitted crucial information that is always included in reputable research, such as a statement of any financial conflicts of interest that the authors might have.