Direct answer: AHAs (glycolic, lactic acid) are water-soluble and work on the skin's surface, improving texture and tone. BHA (salicylic acid) is oil-soluble and can penetrate into the pore itself, making it the relevant choice for congestion and breakouts. They're not interchangeable: an AHA won't fix clogged pores, and a BHA isn't the right tool for surface texture alone.
AHA and BHA get grouped together constantly, usually under a single word: exfoliant. They are related in function and completely different in mechanism, and using the wrong one for your skin's actual need is one of the most common reasons an exfoliating routine underperforms.
What do AHAs actually do?
Alpha hydroxy acids, including glycolic acid and lactic acid, are water soluble. They work on the surface of the skin, dissolving the bonds between dead skin cells so they shed more evenly. This improves texture, supports a more even tone over time, and helps other products penetrate more effectively because they are no longer working through a layer of built up dead skin.
Glycolic acid has the smallest molecular size of the common AHAs, which allows it to penetrate slightly deeper and work faster. Lactic acid is larger and gentler, and it carries a mild humectant effect alongside its exfoliating action, which makes it a more forgiving entry point for skin that has not used acids before.
What does BHA actually do?
Beta hydroxy acid, most commonly salicylic acid, is oil soluble rather than water soluble. This is the entire reason it exists as a separate category. Because it dissolves in oil, it can penetrate into the pore itself, where AHAs cannot reach, making it the relevant choice for congestion, blackheads, and oil related breakouts rather than surface texture.
If your concern is texture and tone, an AHA is doing the right job. If your concern is clogged pores and breakouts, a BHA is solving a different problem, and no amount of AHA will address it, because the two acids are not interchangeable substitutes for each other.
Why the confusion causes real problems
Someone using an AHA for oily, congestion prone skin may see improved texture without any real change in breakouts, and conclude the entire category of exfoliants does not work for them. The acid was never treating the actual issue.
The Seraé approach
The Midnight Concentrate uses lactic acid, positioned as the gentler entry point for surface renewal and tone. The Exfoliant Toner uses glycolic acid for a faster acting surface effect. Both are AHAs, chosen deliberately because Seraé's current formulation focus is surface renewal and tone, not pore level congestion. If your primary concern is active breakouts rather than texture, that is a different conversation, and worth having with a dermatologist before adding any acid to your routine.
Frequently asked questions
What's the difference between AHA and BHA?
AHAs are water-soluble and work on the skin's surface (texture, tone). BHA is oil-soluble and can penetrate into the pore, making it the relevant choice for congestion and breakouts.
Should I use AHA or BHA for breakouts?
BHA (salicylic acid), because it's oil-soluble and can penetrate into the pore itself, where AHAs can't reach.
What's the difference between glycolic acid and lactic acid?
Both are AHAs. Glycolic acid has a smaller molecular size and penetrates deeper, working faster. Lactic acid is larger, gentler, and carries a mild humectant effect, making it a better entry point for acid-new skin.
Can I use AHA and BHA together?
For a specific concern involving both texture and congestion, this is worth confirming with a dermatologist rather than combining actives without guidance.
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