BHA Leave-On Limits and Why They Differ From AHAs

Salicylic acid and glycolic acid get lumped together constantly in marketing copy, "exfoliating acids," as if they're one category with one rule. They're chemically distinct compound classes (beta hydroxy versus alpha hydroxy), and treating them as interchangeable when you're checking concentration limits is how a formula ends up screened against the wrong ceiling entirely.

They're not the same acid family

Salicylic acid is the BHA (beta hydroxy acid) most commonly used in cosmetics. Glycolic and lactic acid are AHAs (alpha hydroxy acids). The "beta" versus "alpha" difference isn't just naming trivia, it reflects a real structural difference in where the hydroxyl group sits relative to the carboxylic acid group, and that structural difference is part of why regulators and safety assessments treat the two categories separately rather than as one interchangeable "acid exfoliant" bucket.

Why the limits get applied differently

Concentration ceilings for cosmetic ingredients are set based on the specific substance's own safety and use profile, not on a general "acid" category. Salicylic acid also has its own additional wrinkle: at higher concentrations or with drug-type claims (like acne treatment claims), it can shift from being regulated as a cosmetic ingredient to being treated as a drug ingredient, since anti-acne products are typically regulated as drugs rather than cosmetics. This is a separate consideration from a straightforward concentration ceiling and one that's easy to trip over if your marketing copy makes an acne claim without you realizing that claim changes the regulatory category of the whole product.

Glycolic and lactic acid don't carry that same drug-claim trap in the same way, since exfoliation and general skin-conditioning claims are more squarely cosmetic territory, but they still have their own specific concentration considerations tied to their own ingredient profile.

The mistake to avoid

Because a lot of DIY and small-batch formulation resources talk about "AHA/BHA limits" as if there's one shared number, it's easy to look up a limit for glycolic acid and assume it applies equally to salicylic acid, or vice versa. It doesn't. Each ingredient's restriction, if one applies, is tied to that specific INCI entry on the Hotlist, not to the broader chemical family it belongs to.

A practical way to keep this straight:

• Look up salicylic acid by its own INCI name and CAS number, separately from any AHA
• Look up glycolic acid, lactic acid, or any other AHA you use the same way, individually
• Never copy a limit you found for one acid onto a different acid just because both get marketed as "exfoliants"
• If your product makes an anti-acne or blemish-treatment claim alongside salicylic acid, stop and consider whether you've actually created a drug product rather than a cosmetic

A simple reference structure

Ingredient	INCI	Acid class	Watch for
Salicylic acid	Salicylic Acid	Beta hydroxy acid (BHA)	Anti-acne claims shifting product to drug category
Glycolic acid	Glycolic Acid	Alpha hydroxy acid (AHA)	Own specific concentration profile
Lactic acid	Lactic Acid	Alpha hydroxy acid (AHA)	Own specific concentration profile

Always verify the current specific limit for whichever acid you're using directly against the Hotlist or your market's current regulatory source, since these are exactly the kind of numeric details that get updated and shouldn't be assumed from memory or from a general "acids" chart you found somewhere online.

Claims language deserves its own review pass

Separately from concentration, read your own product copy the way a regulator would. "Clears breakouts," "treats acne," and similar language point toward a drug claim regardless of what the label says the product is. "Exfoliates," "smooths texture," and "supports clear-looking skin" stay in cosmetic territory. This distinction matters more for salicylic acid products specifically, since it's the ingredient most associated with acne-treatment marketing.

Getting the right ingredient matched to the right limit, and catching a claim that might reclassify your product, is exactly the kind of check Cosmetic Comply runs automatically. It screens each ingredient against the Hotlist by its specific INCI identity, not by loose category, and flags anything that needs a closer look before a reviewer signs off.