What AHAs and BHAs Actually Do
Both alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs) are chemical exfoliants. Unlike physical scrubs, they dissolve the bonds holding dead skin cells together rather than abrading them off. That distinction matters because chemical exfoliation is generally more uniform and controllable than physical methods.
The key structural difference: AHAs are water-soluble, so they stay at the skin's surface. BHAs are oil-soluble, which allows them to travel through sebum and into the pore lining. That single chemical property is what makes each type better suited to specific skin concerns.
Before adding either to your routine, it's worth understanding how they interact with other actives. For a breakdown of which ingredient combinations can cause irritation or reduced efficacy, see our guide on active ingredients you should not mix.
Breaking Down the AHA Family
The most widely used AHAs in skincare are glycolic acid and lactic acid. Glycolic acid has the smallest molecular size of the group, which means it penetrates more readily and tends to be more potent — but also more likely to cause irritation at higher concentrations. Lactic acid is larger, penetrates more slowly, and is generally considered gentler, making it a reasonable starting point for those new to chemical exfoliation.
Other AHAs — mandelic, malic, and tartaric acid — appear in some formulas, often blended to moderate the overall effect. Mandelic acid, derived from almonds, is particularly well regarded for sensitive or darker skin tones because its larger molecule size reduces the risk of post-inflammatory hyperpigmentation.
AHAs also have a secondary benefit beyond exfoliation: at certain concentrations, they can support the skin's moisture-binding capacity. Lactic acid in particular has a recognized humectant effect. If you're curious how humectants fit into a broader routine, our piece on how hyaluronic acid works and its limits is a useful companion read.
New to AHAs? Start Low and Slow
If you've never used an AHA before, begin with a lactic acid product at 5% or below, used two to three times per week. Give your skin at least two to three weeks to adjust before increasing frequency or concentration. Redness, peeling, or stinging that persists beyond the first few minutes of application is a signal to reduce use — not push through.
Understanding BHAs
Salicylic acid is the BHA you'll encounter in virtually every over-the-counter product marketed for acne or congested pores. Its oil solubility allows it to cut through excess sebum inside the follicle, loosening debris and dead cells that contribute to blackheads, whiteheads, and inflammatory breakouts.
Salicylic acid also has anti-inflammatory properties, which sets it apart from AHAs — it can calm redness while exfoliating. This makes it a practical option when breakouts are accompanied by visible irritation. Typical effective concentrations in OTC products range from 0.5% to 2%.
A less common BHA is betaine salicylate, derived from sugar beets, which is gaining traction in some formulations as a milder alternative. It functions similarly to salicylic acid but may cause less dryness at comparable concentrations.
| AHAs | BHAs | |
|---|---|---|
| Solubility | Water-soluble | Oil-soluble |
| Primary action | Surface exfoliation | Pore-penetrating exfoliation |
| Common examples | Glycolic acid, lactic acid, mandelic acid | Salicylic acid, betaine salicylate |
| Best skin type | Dry, dull, or aging skin | Oily, acne-prone, or congested skin |
| Anti-inflammatory effect | Minimal | Yes (salicylic acid) |
| Sun sensitivity increase | Yes — SPF required | Yes — SPF required |
| Gentlest option | Mandelic or lactic acid | Betaine salicylate |
Matching the Right Acid to Your Skin
The practical guidance here isn't complicated, but it does require some honest assessment of your skin's behavior:
- Dry or dehydrated skin: AHAs, particularly lactic acid, address the surface buildup that makes dry skin look flaky and dull without stripping the moisture barrier as aggressively.
- Oily or acne-prone skin: BHAs reach where the problem originates — inside the pore — making salicylic acid more effective for reducing blackheads and preventing breakouts than a surface-acting AHA.
- Combination skin: Some formulas offer a blend of both. Alternatively, you can use a BHA on oilier zones and an AHA elsewhere, though this requires attention to avoid over-exfoliating.
- Sensitive skin: Start with mandelic or lactic acid at low concentrations (around 5%) a few times per week before considering any BHA.
Don't Over-Exfoliate — It Backfires
Using AHAs and BHAs daily, or layering multiple exfoliating products in the same routine, can compromise the skin barrier — leading to increased sensitivity, breakouts, and redness. More exfoliation is not always better. If your skin feels tight, raw, or unusually reactive, scale back frequency and focus on barrier-supporting products like gentle moisturizers before reintroducing acids.
Application, Frequency, and Sun Protection
Both AHAs and BHAs increase photosensitivity by removing the outermost layer of skin. This is not optional context — applying either without daily broad-spectrum sunscreen meaningfully increases your risk of sun damage and can worsen the hyperpigmentation you may be trying to correct.
Most dermatologists suggest starting with two to three uses per week and assessing tolerance before increasing frequency. Products vary widely in concentration and formulation, so more frequent use of a lower-concentration product is generally safer than jumping straight to a high-potency formula daily.
Apply exfoliating acids after cleansing and before heavier serums or moisturizers. Allow a short wait time before layering other actives — especially anything with a significantly different pH — to let the acid do its work and reduce the chance of irritation. For a deeper dive into which ingredient pairings to avoid entirely, refer back to our guide on mixing active ingredients.
This article provides general skincare education and is not a substitute for advice from a licensed dermatologist. If you have persistent skin concerns, consult a qualified healthcare professional.
