BHA vs AHA: What's the Difference and Which Do You Need?
Posted on May 11 2026
Chemical exfoliation has largely replaced physical scrubs as the preferred approach for removing dead skin cells and improving skin texture — and for good reason. When done correctly, chemical exfoliation is more controlled, more consistent, and significantly less likely to cause micro-tears or irritation than abrasive particles.
But “chemical exfoliant” is not one thing. BHAs and AHAs work differently, penetrate to different depths, and suit different skin concerns. Understanding the distinction will help you choose the right one — or know when using both makes sense.
What AHAs Are
Alpha-hydroxy acids are water-soluble acids derived primarily from fruits and dairy. The most common in skincare are:
- Glycolic acid: The smallest molecule, deepest penetration, most studied
- Lactic acid: Larger molecule, gentler, also hydrating
- Mandelic acid: Largest AHA molecule, gentlest and most suitable for sensitive skin
AHAs work by dissolving the bonds between dead skin cells on the surface (the stratum corneum), allowing them to shed more readily. They improve skin texture, reduce the appearance of fine lines, brighten uneven skin tone, and — with consistent use — stimulate collagen production.
Because they are water-soluble, AHAs stay primarily on the skin surface and upper layers of the epidermis. They do not penetrate significantly into pores.
What BHAs Are
Beta-hydroxy acid — salicylic acid is essentially the only BHA used in skincare — is oil-soluble. This is the critical distinction. Because it dissolves in oil rather than water, salicylic acid can penetrate through the sebum layer lining the inside of pores, reaching the environment where blackheads, whiteheads, and congestion develop.
BHAs are also anti-inflammatory and mildly antibacterial, making them useful not just as an exfoliant but as a targeted treatment for acne-prone skin.
Which Is Right for Your Skin Concern?
Rough texture, dullness, fine lines: AHA. The surface-level exfoliation and collagen-stimulating effects of glycolic or lactic acid are well-suited for these concerns.
Blackheads, congestion, enlarged pores: BHA. Salicylic acid’s ability to penetrate into the pore is what makes it specifically effective here. An AHA will not address the content of a clogged pore the way a BHA can.
Uneven skin tone, hyperpigmentation: AHA (particularly glycolic and lactic acid, which accelerate cell turnover and fade pigmentation). A vitamin C serum and SPF alongside your AHA routine will significantly amplify this effect.
Acne-prone, oily skin: BHA primary, with AHA as a secondary option for texture between BHA sessions. The BHA + AHA Skin Perfector by SW1 Shop combines both in a formulation designed for congested, textured skin.
Dry or sensitive skin: Lactic acid or mandelic acid (gentle AHAs) are better starting points than salicylic acid, which can be more drying. Low-concentration lactic acid is one of the most tolerable exfoliating actives available.
Keratosis pilaris: Lactic acid is one of the most evidence-supported options. The combined humectant and exfoliating properties of lactic acid address the rough, bumpy texture characteristic of KP on arms and thighs.
How to Use Chemical Exfoliants Safely
Start with lower concentrations. The most common mistake is beginning with a high-percentage AHA and overloading the barrier immediately. Start with 5–8% glycolic acid or lactic acid; start BHA at 1–2%.
Frequency matters more than concentration. Two to three times a week is sufficient for most people. Daily exfoliation is unnecessary and risks barrier compromise unless you have built significant tolerance over time.
Never exfoliate compromised skin. If your barrier is already irritated, sensitised, or damaged, chemical exfoliation will make it worse. Focus on barrier repair first.
Always use SPF the morning after an AHA. AHAs increase photosensitivity significantly. Without SPF, you undermine the pigmentation benefits and risk new sun damage on freshly exfoliated skin.
Do not stack exfoliants unnecessarily. If you are using a BHA and an AHA in the same routine, use them on alternate evenings rather than both at once — particularly when starting out.
FAQ
Can I use BHA and AHA together? Yes, but structure is important. On alternating evenings is the safest approach when building tolerance. As your skin adapts, some people use BHA two evenings and AHA one evening per week, or use a combined product (like SW1 Shop’s BHA+AHA Skin Perfector) that formulates both at compatible levels.
Which is stronger — BHA or AHA? They address different things, so “stronger” depends on the concern. For surface exfoliation and anti-ageing, higher-concentration AHAs (10–20% glycolic) are typically more potent. For pore-clearing, BHA is superior regardless of AHA concentration.
Can I use vitamin C with AHA? Not in the same step, ideally — both operate at low pH and stacking them can be too aggressive. Use vitamin C in the morning (under SPF) and AHA in the evening.
What is the difference between salicylic acid and lactic acid? Salicylic acid (BHA) is oil-soluble and clears pores; lactic acid (AHA) is water-soluble and exfoliates the skin surface. They are suited to different concerns and can be used in the same routine at different times.
For professional exfoliation treatments — chemical peels, microdermabrasion, and more — SW1 Clinic offers medically supervised options with stronger concentrations than are available over the counter. SW1 Spa provides gentler exfoliating facial treatments for regular maintenance.
