AHAs (alpha hydroxy acids, like glycolic and lactic acid) work mainly on the skin’s surface, dissolving the “glue” between dead skin cells. BHAs (mainly salicylic acid) are oil-soluble, so they can get down into pores and help clear the debris that contributes to blackheads and clogged pores. Both exfoliate; they just work in different places.
What exactly is an AHA?
AHA stands for alpha hydroxy acid — a group of water-soluble acids that loosen the bonds holding dead skin cells together on the surface of the skin. The most common ones in skincare are glycolic acid (from sugar cane), lactic acid (originally from milk, now usually made synthetically), and less commonly mandelic acid.
Because AHAs are water-soluble, they mostly work on the top layer of skin. Regular, gentle use can help skin look smoother and can fade some post-acne marks over time, though nothing removes marks quickly and results vary a lot from person to person. AHAs are also widely used for general texture and dullness, not just acne, which is part of why they turn up in so many different products.
What exactly is a BHA?
BHA stands for beta hydroxy acid, and in practice this almost always means salicylic acid. The key difference from AHAs is that salicylic acid is oil-soluble. That means it can move through the oily lining of a pore rather than staying on the surface, which is why it’s so often recommended specifically for oily and acne-prone skin.
Inside the pore, salicylic acid can help break down the mix of oil and dead skin cells that contributes to blackheads and closed comedones. For a fuller explanation of how this actually works, this plain-language look at what salicylic acid does goes into more detail.
What’s the real difference between AHAs and BHAs?
The core difference is solubility, and that drives everything else: AHAs are water-soluble and act mainly on the surface, while BHAs are oil-soluble and can penetrate into oily pores. This is why BHAs are usually favoured for blackheads and clogged pores, while AHAs are often favoured for surface texture, dullness and mild discolouration.
A few other practical differences:
- AHAs can make skin more sensitive to sun; sunscreen matters even more with regular use.
- BHAs tend to be slightly less irritating for some people because they don’t draw as much water out of the skin, though this varies person to person.
- AHAs are often used on the body and face for general texture; BHAs are more specifically associated with oily, congested, acne-prone skin.
- Some products combine both, aiming at surface texture and pore congestion at the same time — which can be effective for some people, but also means twice the potential for irritation if introduced carelessly.
Which one is better for acne?
Neither is universally “better” — it depends on what’s actually happening in the skin, and that’s genuinely something worth discussing with a pharmacist or dermatologist rather than guessing. As a general pattern, BHA (salicylic acid) is more often reached for when blackheads, closed comedones and oily congestion are the main concern, because it can work inside the pore itself.
AHAs are more often used for overall texture, dullness, or fading of marks left behind after breakouts have healed, rather than for active congestion. Some routines use both, at different times or on different areas, but that’s a decision best made slowly and one product at a time — not by adding several new actives in the same week. Introducing one product at a time makes it much easier to tell what’s actually helping and what’s causing irritation.
Can AHAs and BHAs be used together?
They can, and plenty of commercial products combine both, but layering strong actives increases the chance of irritation, dryness and peeling — especially for skin that’s already using something like a retinoid or benzoyl peroxide. There’s no fixed rule that says combining them is unsafe, but there’s also no rule that says more exfoliation is automatically more effective.
People sometimes assume that if a small amount helps, more must help faster. That’s one of the more common exfoliation myths, and it’s worth reading about what over-exfoliating actually does to skin before stacking multiple acids in one routine. Overdoing it can strip the skin barrier faster than it can repair itself, which tends to make skin look worse, not better, and can take a while to settle down again.
Do AHAs or BHAs cause purging?
They can contribute to a short adjustment period where skin looks slightly worse before it improves, since exfoliation speeds up cell turnover and can bring existing congestion to the surface faster. This is different from a reaction where skin becomes newly irritated, itchy, or breaks out in areas it never usually does.
Because these two things look similar at first but mean different things, it’s worth reading the difference between skin purging and a bad reaction before deciding whether to push through discomfort or stop using a product. When in doubt, easing off and asking a pharmacist or dermatologist is a reasonable, unremarkable step — not an overreaction.
Do these ingredients replace other acne treatments?
Not really — they sit alongside other options rather than replacing them. AHAs and BHAs are exfoliants; they work differently from ingredients like benzoyl peroxide, which targets acne-causing bacteria, or retinoids, which affect how skin cells form and shed. What benzoyl peroxide actually does and the difference between retinol and prescription retinoids are useful comparisons if trying to work out what a full routine might look like.
For more persistent, painful, or scarring acne, or acne that’s affecting mood and confidence, exfoliating acids are not a substitute for medical treatment. Options like prescription-strength retinoids, oral antibiotics, hormonal treatments or isotretinoin are things a doctor can discuss and monitor properly — they are not something to source or dose independently, and a GP or dermatologist is the right person to weigh them up. Asking for help with acne early is a normal step, not an overreaction.
How should someone actually try an AHA or BHA?
Slowly, and one at a time. Patch-testing a new product before applying it to the whole face is a simple way to catch a reaction before it becomes a bigger problem — this guide to patch testing covers how to do it properly. After that, most people start with lower frequency (a few times a week rather than daily) and watch how skin responds over several weeks, since judging a new skincare product fairly takes longer than most people expect.
A few other things worth keeping in mind:
- Moisturiser still matters when using acids — exfoliation without support can leave the skin barrier compromised. Acne-prone skin and moisturiser covers why skipping it isn’t the shortcut it seems.
- Sunscreen becomes more important, not less, since exfoliated skin can be more reactive to UV. Sunscreen and acne-prone skin explains the reasoning.
- If the skin barrier already feels damaged, tight, or is stinging with normal products, it may be worth pausing acids altogether and reading about rebuilding a damaged skin barrier first.
Where to go from here
AHAs and BHAs are two of the most talked-about ingredients in skincare, but they’re only two pieces of a much larger picture that includes oil production, hormones, genetics and the skin barrier. The Ingredients Explained hub covers other actives in the same plain style, and the Acne Basics hub is a reasonable starting point for understanding why acne forms in the first place, before deciding which ingredient might be worth trying next.
Acne Cut publishes general information about skin, not medical advice. We are writers and researchers, not dermatologists, doctors or pharmacists. Acne varies enormously from person to person, and what suits one person’s skin can irritate another’s. If your acne is painful, scarring, getting worse, or affecting how you feel day to day, speak to a doctor or a dermatologist — that is a normal thing to do and it is what they are there for.