Combining an AHA and a BHA in One Formula Legally

Dual-acid exfoliants are everywhere right now, glycolic paired with salicylic in one toner, lactic and salicylic in one serum, and the formulation logic makes sense: an AHA working on the skin surface, a BHA getting into pores. What trips people up is treating this as one exfoliant decision instead of two separate ingredients, each with its own concentration ceiling, that happen to share a bottle.

Why you can't just split the difference

It's tempting to think "if the limit for glycolic acid alone is some percentage, and the limit for salicylic acid alone is some percentage, I'll just use half of each and call it balanced." That's not how concentration limits work. Each acid has its own restriction, evaluated independently, because the safety concern behind each limit relates to that specific ingredient's own irritation and penetration profile, not a shared "total acid" budget.

Practically, that means you check your AHA concentration against its limit, and separately check your BHA concentration against its own limit, and both need to pass on their own terms. Using less of each doesn't average out to some combined safe zone, and a formula can absolutely fail if you get generous with one acid because you assumed you'd "saved room" by going light on the other.

What actually varies by market and needs checking

Concentration limits for cosmetic acids differ across regulatory markets, and they can also depend on the exact form of the acid, the pH of the finished product, and whether the product is rinse-off or leave-on. Because these specific numeric thresholds shift by jurisdiction and get updated periodically, this is exactly the kind of detail to verify against the current hotlist or regulation for whichever market you're filing in, rather than relying on a number you saw in an old forum thread or a competitor's marketing copy.

What's safe to say generally: both AHA and BHA use in leave-on cosmetics is typically capped well below the concentrations used in professional or medical peels, and going over the cosmetic-appropriate range for either ingredient is one of the more common reasons dual-acid formulas get flagged during ingredient review.

A structured way to check your formula

Rather than eyeballing it, work through each acid as its own line item:

Step	AHA (example: Glycolic Acid)	BHA (example: Salicylic Acid)
INCI name confirmed	Glycolic Acid	Salicylic Acid
CAS number confirmed	Check current reference	Check current hotlist entry
Concentration in finished product	Calculate from raw material % and use level	Calculate from raw material % and use level
Applicable limit for this market	Verify current limit	Verify current limit
Product type (leave-on vs rinse-off)	Confirms which limit applies	Confirms which limit applies
Pass or flag	Independent check	Independent check

Do this for each acid separately, and don't let a comfortable margin on one create false confidence about the other.

A formulation habit that helps

Build your percentage math the same way you'd document any other active: note the raw material's actual acid content (some AHA raw materials are sold pre-diluted, not as 100% acid), then calculate what percentage of your finished formula that acid represents once your use level and the raw material's actual concentration are both factored in. Skipping the raw-material-dilution step is a quiet way formulas end up over or under their real acid percentage without anyone noticing until a filing gets flagged.

Where this fits into a broader ingredient check

Dual-acid products also tend to carry other actives worth flagging on the same pass, since a lot of dual-exfoliant formulas also include niacinamide, retinol derivatives, or fragrance components that carry their own limits. Treat the whole formula review as a line-by-line exercise rather than focusing exclusively on the acids because they're the obvious active.

This is precisely the kind of multi-ingredient concentration math that benefits from a second set of eyes and a systematic check rather than a mental tally. Cosmetic Comply screens every ingredient in a formula independently against the current prohibited and restricted lists, including concentration-limited actives like AHAs and BHAs, with a confidence score on each one, and a real reviewer checks the result before the notification goes in. That independent, ingredient-by-ingredient approach is exactly the discipline dual-acid formulas need.