AHA or BHA: Which Exfoliating Acid Is Right for Your Skin?

Key Takeaways

• AHAs are water-soluble. They work at the surface, which is why they suit dullness, uneven-looking texture, a rough-looking surface, and the appearance of fine lines.
• BHAs are oil-soluble. They can reach inside the pore, which is why they suit congestion, blackheads, visibly enlarged pores, and oilier-looking skin.
• Salicylic Acid is the BHA you’ll actually see. The FDA notes that from a chemist’s perspective it is not a true Beta Hydroxy Acid, though the label stuck.
• You don’t have to choose. Well-formulated products routinely combine both, which usually beats layering two separate treatments.
• Concentration and pH shape the outcome, not the acronym. And sunscreen is especially important with either: FDA research found four weeks of AHA use raised sensitivity to UV-induced skin reddening by 18%.

Where AHAs and BHAs Actually Go in Your Skin

Most people come to this question wanting to know which acid is stronger. That is rarely the thing that decides it. The more useful question is where you need the work done, because AHAs and BHAs don’t go to the same place.

Alpha Hydroxy Acids are water-soluble, so they work across the surface of the skin, helping loosen the bonds between dull-looking, spent cells. Beta Hydroxy Acids are oil-soluble, so they can move through sebum and reach inside the pore. Almost everything else about choosing between them follows from that one difference.

Below: how each family works, which one suits which skin, why the answer is often both, and what the FDA and the American Academy of Dermatology say about using them safely.

What Are AHAs (Alpha Hydroxy Acids)?

Alpha Hydroxy Acids are a family of ingredients originally derived from fruit, milk, and sugar. Because they dissolve in water, they stay where water goes: across the surface, where they help loosen the glue holding spent cells to one another. What you see afterward is a smoother-looking surface that can reflect light better, which is often what people mean when they say their skin looks brighter. The FDA’s own guidance on AHAs describes the effect plainly: “AHA-containing products cause exfoliation, or shedding of the surface skin.”

The AHAs differ mostly by molecule size, and size largely governs how deep and how fast an ingredient travels. Think of sand through a sieve.

Glycolic Acid is the smallest at 76.05 g/mol, and that small molecule is why it reaches the stratum corneum and epidermis most readily. Speed has a cost. In a comparative study of AHAs, the l(+) form of Lactic Acid matched Glycolic Acid on results while drawing fewer consumer complaints, and at higher concentrations it was reported to sting less. Lactic Acid is next at 90.08 g/mol and also behaves as a humectant, drawing in water while it works. Tartaric Acid sits at 150.09 g/mol and Citric Acid at 192.12 g/mol, both often used to help set a formula’s pH as well as to exfoliate. Mandelic Acid, at 152.15 g/mol, is the one to reach for on reactive skin, since it is less prone to causing irritation than the other AHAs.

What Are BHAs (Beta Hydroxy Acids)?

Beta Hydroxy Acids are oil-soluble, and that single property is the whole argument for them. Sebum sits in the pore, and a water-soluble ingredient can’t easily travel through it, so a BHA is the one that can reach the pore lining and help clear the mix of oil and spent cells that makes pores look larger and darker.

In practice, there’s one BHA you’ll see on a label. The FDA lists Salicylic Acid, Beta Hydroxybutanoic Acid, Tropic Acid, and Trethocanic Acid as BHA ingredients, and then adds that “currently, the BHA most commonly used in cosmetics is salicylic acid.” Willow Extract and Sodium Salicylate are the related substances you’ll sometimes see standing in for it.

One footnote explains why chemists and beauty editors seem to disagree. The FDA’s own page on Beta Hydroxy Acids carries this line: “From a chemist’s perspective, salicylic acid is not a true BHA. However, cosmetic companies often refer to it as a BHA and, consequently, many consumers think of it as one.” What you’re actually buying is the oil solubility.

What Is the Real Difference Between AHA and BHA?

Set side by side, the two families sort themselves quickly.

	AHAs	BHAs
Solubility	Water-soluble	Oil-soluble
Where they work	Across the skin’s surface	The surface, and inside the pore
What you’ll see on a label	Glycolic, Lactic, Mandelic, Tartaric, and Citric Acids	Salicylic Acid
Tends to suit	Dullness, uneven-looking texture, a rough-looking surface, the appearance of fine lines	Congestion, blackheads, visibly enlarged pores, excess oil
Skin that tends to prefer them	Normal, dry-looking, and sun-exposed skin	Oily-looking, combination, and blemish-prone skin
Sun protection	FDA recommends a Sunburn Alert statement on AHA cosmetics	The CIR Expert Panel recommends daily sun protection where sensitivity is expected

Which Acid Is Right for Your Skin?

Work from what your skin is doing right now. It changes the answer more often than your skin type does.

• Dullness, uneven-looking texture, and the appearance of fine lines: an AHA, with Glycolic or Lactic Acid doing most of the work. Surface cell buildup scatters light and can make skin look tired, and it sits where AHAs work.
• Blackheads, congestion, and pores that look enlarged: a BHA. This is the one case where an AHA doesn’t reach the concern as easily.
• Oily-looking or blemish-prone skin: a BHA, and preferably one you can use consistently rather than aggressively.
• Sensitive or reactive skin: The AAD notes that people with dry, sensitive, or acne-prone skin “may prefer just a washcloth and a mild chemical exfoliator,” since mechanical scrubs are often too irritating.
• Deeper complexions, or skin that marks easily: Go slower. The AAD advises avoiding strong chemical or mechanical exfoliation on deeper complexions, or if you notice dark spots after burns, bites, or breakouts, because aggressive exfoliation can lead to increased pigmentation.
• Rough- and bumpy-looking skin on the arms and legs: an AHA blend built for the body, where the skin is thicker and forgives more than the face does.

What About PHAs, the Third Option?

Polyhydroxy Acids rarely make it into the AHA-versus-BHA conversation, though they solve a real problem. Gluconolactone and Lactobionic Acid, the two most common, share the AHAs’ chemistry but carry a far larger molecule. Lactobionic Acid weighs 358.30 g/mol, nearly five times the size of Glycolic Acid.

That size is the point. PHAs carry larger molecules than either AHAs or BHAs, which makes them less likely to penetrate deeply, so the exfoliation is gentler and the stinging that puts people off acids largely doesn’t happen. PHAs also behave as humectants, holding water at the surface while they work, which is why they can suit skin that has found acids too much in the past.

Lactobionic Acid is featured in our Resurfacing Compound alongside Glycolic and Mandelic Acids, which is a deliberate choice. Pairing a fast, small ingredient with a slow, large one lets one formula work at more than one depth without pushing any of them hard.

Can You Use AHA and BHA Together?

Yes, and for most people it is the better answer. The FDA notes that combinations of AHAs and BHAs have been appearing in skin care for years, and the reason is straightforward: Skin rarely has only one thing going on. Congestion around the nose and dullness across the cheeks are different concerns, and one formula can help with both.

What we’d steer you away from is layering two separate treatments on the same night. That’s where visible irritation can come from, and it’s the opposite of how we think about a routine.

That’s the thinking behind both of our resurfacing formulas. For daily maintenance your skin gets Resurfacing Compound, the Holy-Grail Multitasking Serum, built on Glycolic, Lactobionic, and Mandelic Acids with a stable Retinyl Ester and left on. For the weekly reset, Resurfacing Flash Peel is the one that carries both families: Glycolic Acid leads the formula, with Citric, Salicylic, and Tartaric Acids behind it, and you rinse it off after up to 10 minutes. Both are powered by proprietary SIREN Capsule Technology™, so what your skin gets is concentrated where it is asking for it rather than spread evenly across skin that was behaving already.

How Do You Use Exfoliating Acids Safely?

Acids are one of the few categories where doing less genuinely gets you more.

• Wear sunscreen, and keep wearing it afterward. FDA research found that after four weeks of AHA use, volunteers’ sensitivity to UV-induced skin reddening rose by 18%. The agency recommends AHA cosmetics carry a Sunburn Alert advising sunscreen, protective clothing, and limited sun exposure “while using this product and for a week afterwards.” The reassuring half of the same research is that the effect reverses within about a week of stopping.
• Patch test first. The FDA’s guidance on BHA products is to test on a small area before applying to a large one, and to stop and consult a physician if you get irritation or prolonged stinging.
• Moisturize after. Exfoliating can be drying, and the AAD’s advice is to “apply moisturizer immediately after exfoliating to keep your skin healthy and hydrated.”
• Let frequency follow strength. The AAD puts it plainly: The more aggressive the exfoliation, the less often it needs doing. A gentle daily formula and a strong weekly one are both reasonable. Daily use of a strong one is where people get into trouble.
• Don’t exfoliate broken or sunburned skin. Wait until the moisture barrier has recovered.

Why Concentration and pH Matter More Than the Acronym

The FDA states that the extent of exfoliation “depends on the type and concentration of the AHA, its pH, and other ingredients in the product.” Four variables, and the ingredient’s name is only one of them.

The numbers behind that are public. Reviewing industry studies, the Cosmetic Ingredient Review Expert Panel concluded that Glycolic and Lactic Acids are safe for consumer use when the concentration is 10% or less, the finished product has a pH of 3.5 or greater, and the formula either protects against increased sun sensitivity or tells you to. pH matters more there than the percentage does. The same ingredient at the same percentage can behave like a different one depending on where the formulator lands the pH, which is why Resurfacing Flash Peel lists Sodium Hydroxide directly behind its Glycolic Acid.

It’s why we’ve never been interested in selling you an acid for every concern. A formula that holds Glycolic, Lactobionic, and Mandelic Acids in the right proportions delivered precisely will usually do more, and ask less of your skin, than a shelf of single-ingredient products used in sequence. Our guide to exfoliating safely at home covers technique, and our at-home chemical peel guide covers what changes when you go stronger and less often.

Frequently Asked Questions

Is Salicylic Acid an AHA or a BHA?

A BHA, by industry convention. The FDA lists Salicylic Acid as the BHA most commonly used in cosmetics, while noting that from a chemist’s perspective it is not a true Beta Hydroxy Acid. What matters in practice is that it is oil-soluble, which is what lets it work inside the pore.

Is Glycolic Acid an AHA?

Yes, and it is the smallest one at 76.05 g/mol. That size is why it acts quickly and travels furthest. Lactic Acid is an AHA too, slightly larger at 90.08 g/mol, and at higher concentrations its l(+) form stings less than Glycolic Acid does.

Can you use AHA and BHA together?

Yes. The question that matters is whether to use them in one formula or two products. One well-balanced formula, like the Resurfacing Compound, is designed to be kinder to the skin than layering two separate treatments on the same night.

Is AHA or BHA better for the look of dark spots?

An AHA. Visible discoloration sits in the upper layers of the skin, which is where water-soluble ingredients work. Mandelic Acid is often the gentler starting point on skin that marks easily, since its larger molecule slows the whole process down.

Which acid can help with rough- and bumpy-looking skin on the arms and legs?

AHAs, and usually a blend. Body skin is thicker than facial skin and forgives more, which is why body formulas, such as the Resurfacing Body Compound, carry Glycolic, Lactic, and Mandelic Acids alongside Salicylic Acid and Papain, an exfoliating enzyme.

Do you need sunscreen when using AHAs or BHAs?

Yes, with both. The FDA recommends AHA cosmetics carry a Sunburn Alert and advises sun protection for a week after you stop. For BHAs, the CIR Expert Panel’s recommendation is that products either contain a sunscreen or direct you to use sun protection daily. And whichever family you are using, do not exfoliate skin that is already sunburned.

Ready to stop choosing between acids and let one formula do the work? See what’s inside Resurfacing Compound.