Salicylic acid (BHA)

Also known as: beta hydroxy acid, BHA, 2-hydroxybenzoic acid

Salicylic acid is the standard OTC acne acid, an oil-soluble exfoliant that gets into pores in a way water-soluble acids cannot. It has been used medicinally for a very long time and is FDA-monographed for acne at 0.5 to 2%. The surprise for most consumers: a 2020 Cochrane review found the trial evidence behind topical salicylic acid for acne is of low certainty, with high risk of bias, even though clinical experience and peel studies are broadly supportive. It works, but the trial literature is weaker than its reputation.

How it works

Salicylic acid is lipid-soluble, so it penetrates the oil inside pores and dissolves the glue between dead cells lining them, clearing comedones from the inside. It is now understood to work by disrupting cell junctions rather than breaking keratin filaments, and it has mild anti-inflammatory activity related to aspirin, its chemical cousin.

What the evidence says, claim by claim

These are the results measured in studies, not the results shown in ads. Where the research is weak, the grade says so.

For acne

Moderate evidence

The 2020 Cochrane review found salicylic acid trials for acne carried high risk of bias and imprecision, rating the evidence low certainty despite decades of use. Peel-format data are somewhat better: the 2018 BMJ Open systematic review (12 RCTs, 387 participants) found salicylic acid peels performed on par with glycolic and other peels for mild-to-moderate acne. It clearly helps comedonal acne in practice; the grade reflects trial quality, not absence of effect.

Randomized trials support this use, but they are few, small, or short. The effect is probably real. The size of it is less certain.

Topical azelaic acid, salicylic acid, nicotinamide, sulphur, zinc and fruit acid (alpha-hydroxy acid) for acne (Cochrane Database of Systematic Reviews, 2020; systematic-review)
Chemical peels for acne vulgaris: a systematic review of randomised controlled trials (BMJ Open, 2018; systematic-review)

For dullness and texture

Moderate evidence

As a 20 to 30% professional peel, salicylic acid has documented efficacy and safety across Fitzpatrick skin types for texture, photodamage, and comedonal skin, per a 2015 evidence review. Its keratolytic action smooths rough, congested skin within a few sessions. Leave-on 2% products produce milder, slower versions of the same effect.

Randomized trials support this use, but they are few, small, or short. The effect is probably real. The size of it is less certain.

Salicylic acid as a peeling agent: a comprehensive review (Clinical, Cosmetic and Investigational Dermatology, 2015; review)

For dark spots and hyperpigmentation

Limited evidence

Salicylic acid peels are marketed for dark spots and post-acne marks, but a 2024 systematic review of post-inflammatory hyperpigmentation treatments (41 studies, 877 patients) found peels overall had the weakest showing: partial response in only 33.3% of peel-treated patients and poor or no response in 66.7%. It may help mild surface pigment as part of broader acne control, but it should not be the primary pigment treatment.

Only small, short, or lower-quality studies exist. Treat marketing claims about this use with caution.

Post-inflammatory hyperpigmentation: A systematic review of treatment outcomes (Journal of the European Academy of Dermatology and Venereology, 2024; systematic-review)

Risks and what can go wrong

Dryness, peeling, and stinging at 2% leave-on strengths; higher peel strengths can cause frosting and irritation and belong with professionals. Salicylism (systemic toxicity) is a real but rare risk when high concentrations cover large body areas. Small-area facial use in pregnancy is generally regarded as low risk, but many clinicians advise avoiding it; high-strength peels are avoided in pregnancy. Not for use with aspirin allergy.

The practical details

OTC at 0.5 to 2% in cleansers, toners, and spot treatments; 2% leave-on products have the best effect-to-irritation ratio. Professional peels run 20 to 30%. Results on clogged pores appear in 2 to 6 weeks. Oil solubility makes it the better acid for oily and congested skin, while AHAs suit sun damage and texture.