A plant extract sold as 'natural BHA'. Its salicin is not meaningfully converted to salicylic acid in skin; expect a mild soothing extract, not an acne treatment.
Willow bark contains salicin and other salicylates plus polyphenols. Salicin becomes salicylic acid in the gut and liver when you swallow it, but there is little evidence skin converts it to any useful degree, so a willow bark 'BHA' is not equivalent to salicylic acid.
In formulas it adds mild anti-inflammatory and antioxidant activity seen in cell studies.
Evidence is limited to cell and lab studies showing anti-inflammatory effects, plus small manufacturer-run studies of salicin products. No controlled trials show willow bark extract clears acne or exfoliates like salicylic acid.