TL;DR
Salicylic acid is one of the oldest documented therapeutic compounds in medicine, with willow bark records going back to ancient Egyptian, Sumerian, and Greek sources. The active compound was isolated in 1828 by Johann Buchner and refined into pure salicylic acid by Raffaele Piria in 1838. Dermatology adopted it for keratolysis in the late nineteenth century, decades before aspirin existed. Modern BHA serums are a refinement of a 150-year-old skin therapy, not a new invention.
If you sort skincare actives by how long they have been used on human skin, salicylic acid is the runaway winner. The willow-bark remedies that the molecule eventually came from were in use before written medicine existed. The pure compound has been a dermatology staple since the 1880s. The category of beta-hydroxy acid serums on modern shelves is a recent marketing language for a very old therapeutic class.
I think the history matters because the marketing tends to treat BHA as a contemporary technology. It is, in fact, the most thoroughly tested keratolytic in the topical pharmacopoeia, with use across three centuries of dermatology practice.
The ancient willow record
References to willow bark as a pain and inflammation remedy appear in the earliest written medical records. The Ebers Papyrus from approximately 1550 BCE in Egypt describes willow preparations for inflammatory conditions. The Sumerian medical tablets from a similar period list willow alongside other tree-derived remedies. Hippocrates, writing around 400 BCE, recommended willow bark and willow leaf for fever and labor pain. The Roman writer Celsus described similar uses in the first century CE.
These pre-scientific records do not isolate the active compound, but they identify the source material correctly. Willow bark (Salix species) contains salicin, a glycoside that hydrolyzes in the body to salicyl alcohol and then oxidizes to salicylic acid. The traditional remedies were, biochemically, low-dose salicylate therapy.
The chemical isolation
The modern story begins in 1763 when Edward Stone, an English clergyman, presented a paper to the Royal Society documenting his use of dried willow bark to treat fevers. Stone’s methodology was rough by modern standards (he selected willow partly because of the doctrine of signatures, a theory that medicinal plants grow near the diseases they treat), but his clinical observations were correct.
The compound itself was isolated in 1828 by Johann Buchner, a Munich pharmacist, who named it salicin after the willow genus. Raffaele Piria, an Italian chemist working in Paris, converted salicin to salicylic acid in 1838. The Munich chemist Hermann Kolbe synthesized salicylic acid from coal tar derivatives in 1859, which made industrial-scale production feasible.
The next chapter is the aspirin story, which sits adjacent to skincare. Felix Hoffmann at Bayer modified salicylic acid to acetylsalicylic acid in 1897, producing a more tolerable oral form. Aspirin entered the market in 1899 and became one of the most-used drugs in human history. The skincare branch of the salicylate family stayed with the original molecule.
Dermatology adoption
Salicylic acid entered dermatology in the late nineteenth century as a keratolytic. Paul Gerson Unna, the German dermatologist who founded much of the modern field, popularized salicylic acid for hyperkeratotic conditions in the 1880s. The compound was incorporated into Unna’s boot (the medicated zinc paste bandage still used for venous ulcers) and into a range of keratolytic ointments for warts, calluses, corns, and chronic plaque conditions.
The acne indication followed in the early twentieth century. Salicylic acid’s lipid-soluble nature lets it penetrate sebaceous follicles and dissolve the keratin plugs that drive comedonal acne. By the 1920s, salicylic acid was a standard component of acne preparations, often in combination with sulfur. It remained a prescription and over-the-counter staple through the rest of the twentieth century.
The BHA branding
Salicylic acid is technically a beta-hydroxy acid, with the hydroxyl group on the beta carbon relative to the carboxylic acid group. The term beta-hydroxy acid as a skincare marketing category emerged in the 1990s, partly to position salicylic acid against the alpha-hydroxy acid wave that was driving glycolic and lactic acid sales. The biochemistry classification is real; the marketing repositioning was deliberate.
The modern BHA serum category, with low-percentage leave-on products at 1 to 2 percent, traces largely to Paula’s Choice and the late 1990s exfoliating culture. The clinical evidence at these low percentages is solid for acne and pore appearance, though the effect sizes are modest compared with prescription retinoids or stronger acid peels.
The contrarian H2: the higher percentages are not always better
The skincare marketing has trained consumers to read higher percentages as stronger products. For salicylic acid, that mapping does not work cleanly past about 2 percent for leave-on use.
The 2 percent leave-on concentration is where the FDA-approved over-the-counter acne monograph sits and where most of the chronic-use safety data lives. The 0.5 to 1 percent range is where many sensitive-skin products land, with milder effects and lower irritation. The higher concentrations (5, 10, 20, 30 percent) are professional peel territory, used in short application windows under clinical supervision, and not appropriate for daily leave-on use.
The reason this matters is that the over-the-counter market sometimes pushes 5 or 10 percent salicylic acid products as more effective daily-use options. The pharmacology says otherwise. The keratolytic effect saturates at modest percentages with regular use, and the irritation cost climbs faster than the benefit. The 2 percent reference point has been the daily-use sweet spot for nearly a century. The marketing pressure to escalate does not change that.
The real numbers
A 2009 review in the Journal of the American Academy of Dermatology by Arif and colleagues summarized the salicylic acid acne literature across two decades of trials and put the consensus position at 2 percent leave-on for daily comedonal acne management, with effect sizes comparable to benzoyl peroxide 2.5 percent and slightly milder irritation. The 2007 Davis and Callender review in JAAD on chemical peels documented salicylic acid 20 to 30 percent peels in office settings, with 4 to 6 sessions producing meaningful improvement in acne and post-inflammatory hyperpigmentation on skin of color.
The American Academy of Dermatology’s clinical practice guidelines for acne list topical salicylic acid as a reasonable first-line option for mild comedonal acne, ahead of many newer alternatives. The molecule has the longest unbroken track record in over-the-counter acne therapy of any current ingredient.
What this means for your routine
The history points to a few practical anchors. For mild acne and clogged-pore management, 2 percent leave-on salicylic acid is the reference product. Cleanser-strength salicylic acid (typically 0.5 to 2 percent in a rinse-off vehicle) is gentler and useful for sensitive skin or as a first introduction to BHA.
The expected timeline is 2 to 4 weeks for visible reduction in comedonal lesions and 6 to 8 weeks for measurable improvement in pore appearance. Combine with a barrier-supportive moisturizer. Salicylic acid pairs well with niacinamide, retinoids (start one at a time), and azelaic acid. Avoid same-day use with stronger acid peels.
For the broader thinking, see the BHA versus AHA primer, the acne-prone routine guide, and the chemical exfoliation explainer.
FAQ
How old is willow-bark medicine? Documented for at least 3,500 years through Egyptian, Sumerian, and Greek records. The therapeutic use predates the chemical understanding by several thousand years.
Is salicylic acid the same as aspirin? Closely related. Aspirin is acetylsalicylic acid, an acetylated form designed for better oral tolerability. Topical skincare uses the unmodified salicylic acid.
Why is salicylic acid better than glycolic acid for acne? Lipid solubility. Salicylic acid penetrates sebaceous follicles and works directly on the keratin plugs that drive comedonal acne. Glycolic acid is water-soluble and works more on surface keratinization.
Can I use salicylic acid during pregnancy? Low-percentage topical use (2 percent and below) is generally considered acceptable in pregnancy, but consult an obstetrician for individual circumstances. High-percentage peels are typically avoided.
Why does my salicylic acid product sometimes leave a white residue? Salicylic acid has limited solubility in water and can recrystallize on the skin surface, especially in alcohol-light formulations. It is cosmetically annoying but does not affect efficacy.
Tag hub: More on salicylic acid, BHA, and acne-prone routines
Sources
Arif T. Salicylic acid as a peeling agent: a comprehensive review. Clinical Cosmetic and Investigational Dermatology 2015. Davis EC, Callender VD. Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color. JAAD 2007. Mahmoud BH et al. Salicylic acid for acne and hyperpigmentation. AAD.org/” rel=”noopener” target=”_blank”>American Academy of Dermatology Clinical Practice Guidelines for Acne 2016.