Salicylic acid (BHA)

What is salicylic acid?

Salicylic acid is a beta hydroxy acid - a phenolic acid in which the hydroxyl group sits adjacent to the carboxyl group on an aromatic ring. That structure makes it lipophilic, which is the single property that distinguishes it from the alpha hydroxy acids.

How does salicylic acid work?

It loosens the desmosomal connections between corneocytes, allowing them to shed - that is the keratolytic action shared with AHAs. What is not shared is where it can act: because it is oil soluble it partitions into sebum and therefore into the follicular canal, which is where comedones form. An AHA sits on the surface; a BHA gets into the pore. It is also anti-inflammatory, being structurally related to aspirin.

Levels and formulation

Cosmetic use generally runs 0.5% to 2%. Efficacy depends heavily on pH, since only the un-ionised form partitions into sebum - a 2% product at high pH can underperform a 1% product formulated correctly. Vegalab's Clarifying line uses an encapsulated form, which is a reasonable approach to reducing surface irritation while retaining follicular delivery, though encapsulation should come with its own release data.

What does salicylic acid not do?

It does not treat the hormonal drivers of acne, and it will not resolve inflammatory or cystic acne, which needs clinical management. It is not a brightening agent, although clearing surface build-up can make skin look brighter. Overuse produces a damaged barrier and, paradoxically, more oil.

Is salicylic acid safe?

Well tolerated at cosmetic levels. Salicylate absorption is a consideration only with extensive use of high concentrations over large areas. Standard advice is to avoid salicylic acid in pregnancy at other than low, localised cosmetic levels - a question for a clinician.