Skincare Acids: the ultimate guide to BHA, AHA, and PHA (exfoliation)

Exfoliation is an important part of a skincare routine: it helps the skin renew itself, prepares it to absorb subsequent treatments, and contributes to a more even complexion.

However, the differences between the various exfoliating acids are not always well understood, and uninformed use can create more problems than it solves. Let's look in detail at the characteristics of each one and which skin type it is suited to.

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What exfoliating acids are

AHA, BHA, and PHA are ingredients capable of removing dead cells from the skin's surface, promoting renewal. They act through a chemical rather than physical process: they dissolve the bonds between dead skin cells and support cellular turnover.

Some penetrate more deeply, while others have a more superficial action that brightens the complexion and smooths the texture.

Chemical exfoliation and mechanical exfoliation

The two approaches are often confused. Mechanical exfoliation is the type used in scrubs with microbeads and works through friction. It is often more suitable for the body than the face, where circular massage also has a stimulating effect on circulation.

The body scrub from the Relax line is based on salt crystals, with shea butter and hazelnut oil to nourish the skin.

Abrasive sponges also fall into this category: if used too roughly, they can remove more than necessary and irritate sensitive skin.

Chemical exfoliation, on the other hand, works in a more controlled way. No rubbing, no abrasion.

Acids dissolve the bonds that hold dead cells together, allowing them to detach naturally. The result is more even, without micro-injuries, and above all more predictable: you can adjust the intensity by choosing the type of acid, concentration, and frequency. With a scrub, the intensity depends on how hard you press.

There are three main benefits:

• It is uniform, because it works across the entire surface without depending on the pressure of your fingers.
• It is adjustable, allowing you to choose the acid suited to your skin type.
• It is also suitable for sensitive skin: many PHA or mandelic acid-based formulas are gentler than traditional scrubs.

Why acids matter in your routine

They are not an extra for those seeking perfect skin: they support a process the skin already carries out on its own. With age, as well as due to stress, pollution, and sun exposure, cell turnover slows down and the skin appears duller and more uneven.

Regular exfoliation helps improve radiance, refine skin texture, reduce the appearance of light pigmentation and small superficial wrinkles, and make the skin more receptive to subsequent treatments.

AHA, alpha hydroxy acids

They are water-soluble acids, often called fruit acids because of their origin. They act on the skin's surface, improving evenness, cell turnover, and radiance. They are suitable for dull, rough, or lackluster skin.

• Glycolic acid has the smallest molecule, penetrates easily, and visibly smooths the skin. It is also the most potent and the least tolerated by reactive skin.
• Lactic acid is gentler and has a hydrating action: suitable for dry or dehydrated skin.
• Mandelic acid has a larger molecule and therefore penetrates more slowly: it is the best tolerated and suitable for combination and sensitive skin.

The complete comparison of all AHAs — including molecular weights, why citric and tartaric acids almost never truly exfoliate, and the forms in which they are commercially available — can be found in the in-depth guide to alpha hydroxy acids.

Mandelic Enzimatic Soft Peel combines mandelic acid with bromelain and papain, along with chamomile extract and aloe vera: it removes superficial dead skin cells without causing irritation.

BHA, beta-hydroxy acids

They are oil-soluble acids, so they can dissolve sebum and impurities inside the pore. The best known, and practically the only one used in cosmetics, is salicylic acid.

They are the best choice for those with oily or combination skin, enlarged pores, blackheads, or acne-prone skin. Salicylic acid unclogs sebum plugs, reduces the appearance of comedones, and also has a soothing action that is helpful for inflamed blemishes.

It may be too intense for very dry or reactive skin, but in formulations it is adjusted to remain effective without being harsh.

PHAs, the gentlest generation

PHAs — gluconolactone and lactobionic acid — provide superficial exfoliation with a hydrating, barrier-protective action. They also have antioxidant properties.

The technical difference lies in the molecular size: it is much larger than that of AHAs, so it penetrates more slowly and gradually. This results in better tolerance.

They are perfect for anyone who reddens easily or cannot tolerate the tingling sensation of AHAs. In short: they gently enhance radiance, smooth fine lines, strengthen the barrier, and work well alongside other active ingredients.

How much acid can a cosmetic contain?

This is where communication and the regulations tell two different stories, and it is worth distinguishing between them.

Salicylic acid has a binding limit. Regulation (EC) 1223/2009 lists it in Annex III, among restricted substances: a maximum of 3% in rinse-off hair products, 2% in other products, and 0.5% in body lotions, eyeshadows, mascaras, eyeliners, lipsticks, and roll-on deodorants. It is also excluded from products for children under three, except shampoos. That percentage is not a company choice: it is a legal threshold.

For AHAs, the situation is different, and it is the part that almost no one explains. Glycolic and lactic acid do not have a fixed limit in the annexes to the Regulation. There is an opinion from the European scientific committee that, as a precaution, recommends not exceeding 4% glycolic acid at pH ≥ 3.8 and 2.5% lactic acid at pH ≥ 5, with a warning about sun protection. It is a recommendation, not a ban: this is why much more concentrated and perfectly legal formulas are available on the market.

The practical takeaway is clear: when it comes to the percentage of an AHA, you cannot rely on the idea that “there is a legal limit anyway”. What matters is the stated concentration, the pH of the finished formula, and frequency of use. On reactive skin, a 10% product at a low pH is completely different from a buffered 5% product, even if the same ingredient appears on the label.

Professional peeling concentrations, measured in tens of percentage points, fall outside the cosmetic category: they are medical procedures, performed by a dermatologist, and the choice of acid depends on phototype and the risk of post-inflammatory hyperpigmentation.

How to choose based on skin type

Skin that feels tight, marks easily, and tends to become dull needs exfoliation that does not strip it further: this is where PHAs and gentle AHAs such as lactic or mandelic acid come in. Once or twice a week, in the evening, followed by a lipid-rich cream.

When pores are visible and shine predictably appears halfway through the day, BHAs become essential. Pairing them with a mild AHA can improve overall radiance, but proceed with caution: overdoing it leads to more fragile, reactive skin.

If you experience easy redness, stinging, occasional dermatitis, or a compromised skin barrier, it is best to avoid aggressive approaches. PHAs are the safest choice: they exfoliate slowly, hydrate, and improve barrier function instead of weakening it. If the redness is persistent rather than temporary, a dermatologist should assess it: an exfoliant is not the answer to active dermatitis.

If, after reading these lines, it is still unclear which category your skin falls into—which is common, because oily and dehydrated skin at the same time is more common than you might think—that is exactly the question to bring to the counter: LeLang partner pharmacies are trained to assess your skin in person before recommending an exfoliant.

How to incorporate them into your routine

Introduce acids as you would a new ingredient in your diet: gradually and consistently. The practical rule is simple: once or twice a week, with moderate concentrations and only in the evening.

Within ten days or two weeks, your skin gets used to it and you start to see benefits in terms of radiance and smoothness. And one recommendation always applies: the day after exfoliation, sun protection is non-negotiable, because freshly renewed skin is more exposed and can become discolored more easily.

Which active ingredients to combine with acids and which to separate

It’s the question that comes up most often, and it’s also the one surrounded by the most inaccurate information. There’s only one principle to keep in mind: the problem is almost never the “chemical reaction” between two ingredients, but rather the combined effects on the same skin on the same evening.

The signs that you’re overdoing it are always the same: skin that feels tight, stings when you apply cream, becomes red, and looks strangely shiny. It’s not “your skin renewing itself”: it’s a weakened barrier. Stop everything for two weeks, go back to a gentle cleanser and cream, then start again at half the frequency.

Frequently asked questions about exfoliating acids

What are AHA and BHA acids?

AHAs (alpha hydroxy acids) are water-soluble and work on the surface: the main ones are glycolic, lactic, mandelic, citric, and tartaric acids. The BHA used in cosmetics is essentially just one, salicylic acid, which is oil-soluble and can therefore work inside the pore. Put simply: AHAs work on texture and complexion, while BHA works on sebum and pores.

Can I use AHAs and BHAs together?

Yes, and it is actually a combination found in many professional formulas, where the concentrations are already calibrated to work together. What you should avoid is layering two different products on the same evening: in that case, you do not get twice the results—you get a stressed skin barrier. If you use them separately, alternate them on different evenings and still limit use to a total of two or three applications per week.

What should not be used with AHAs and BHAs?

In the same application, it is best not to combine them with retinol and retinoids, benzoyl peroxide, or a physical scrub: these are all stimuli that act on the same front and add up. Pure vitamin C is best used in the morning instead. The old rule about niacinamide should be dispelled, however, as it coexists perfectly well with acids in modern cosmetic formulas.

Which acids can be used during pregnancy?

During pregnancy, it is best to stick to gentler molecules at low concentrations: PHA, lactic acid, and mandelic acid are the most frequently chosen, once a week. Azelaic acid is also considered a well-tolerated active, often used during this stage for melasma-related hyperpigmentation at melasma. Professional peels, high concentrations, and retinoids should instead be postponed. Since this is a special stage, it is worth confirming your routine with your gynecologist or dermatologist.

What is the best acid for a peel?

It depends on who is using it and on which skin. At home, the most sensible acid to start with is mandelic, because its large molecule penetrates slowly and is more forgiving of mistakes; for very reactive skin, move down to PHAs, while for oily skin, move up to salicylic acid. Glycolic acid delivers the fastest results but is also the least forgiving. High-concentration peels, on the other hand, are medical procedures: in that case, the choice of acid is up to the dermatologist, who assesses skin type and the risk of post-inflammatory dyschromia.

Can exfoliating acids be used in summer?

Yes, under two conditions: reduce the frequency and apply sunscreen every morning, without skipping days. Recently exfoliated skin is more exposed to UV rays and, without photoprotection, the real risk is to achieve the opposite effect to the one sought for dark spots.

How do you read the percentage of acid on the label?

In most cases, it isn’t stated at all: the INCI lists ingredients in descending order of quantity, but does not provide percentages. If a brand does not disclose the concentration, the only clue is the acid’s position in the list — if it appears above preservatives and fragrances, it is present in a significant amount. When the percentage is disclosed, it should always be read together with the pH: these are two numbers that only make sense as a pair.

Sources for this article

01 Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products, Annex III — list of substances that cosmetic products may not contain except subject to the restrictions indicated, entry concerning salicylic acid.
02 European Scientific Committee on Cosmetic Products and Non-Food Products Intended for Consumers (SCCNFP), Position paper concerning consumer safety of alpha-hydroxy acids, document SCCNFP/0370/00, 2000: precautionary recommendation on glycolic acid (up to 4%, pH ≥ 3.8) and lactic acid (up to 2.5%, pH ≥ 5), with warnings about eye contact and photoprotection.

On the website: how to exfoliate the skin · alpha hydroxy acids · salicylic acid · mandelic acid · the skin barrier