Glycolic, Lactic or Mandelic Acid: Which AHA Is Right for My Skin?

By Dr Naomi Mackle, dermatology specialist and Medical Director, Adare Dermatology Clinics

Alpha hydroxy acids, or AHAs, are among the most useful ingredients in skincare. They exfoliate the skin chemically rather than by scrubbing, and they sit behind many of the smoother, brighter, clearer results people are looking for. Glycolic acid is the best known, but it is not the only option, and choosing the right one for your skin makes all the difference.

What are AHAs?

AHAs are water-soluble acids that loosen the bonds holding dead skin cells together on the surface of the skin. Once those bonds are loosened, the dead cells shed more easily, pores are less likely to become blocked, and the fresher skin underneath reflects light more evenly.

The three you will see most often are:

• Glycolic acid. The smallest AHA molecule, so it penetrates quickly and deeply. It is a proper little workhorse, and the most effective of the three, but also the one most likely to irritate.

• Lactic acid. A slightly larger molecule, so it works more gently. It also helps the skin hold on to water, which makes it a good choice for dry or rough skin.

• Mandelic acid. A much larger molecule that penetrates slowly and evenly. It is generally better tolerated by sensitive skin and is often a good option for deeper skin tones, where irritation can trigger pigmentation.

Other AHAs, such as citric, malic and tartaric acid, do exist, but in skincare they usually play a supporting role rather than acting as the main active. Their gentler cousins, the polyhydroxy acids (PHAs), are worth knowing about for very sensitive skin.

We sometimes combine glycolic and mandelic acid. Glycolic works quickly at the surface while mandelic works more slowly and evenly, so together they give broad exfoliation without having to push glycolic acid to a higher, harsher strength.

What the evidence actually shows

AHAs have been used in dermatology for decades, and the evidence that they work is consistent. Clinical studies support glycolic acid for acne, pigmentation (including melasma, usually alongside other treatments) and the rough texture and fine lines of sun-damaged skin. With longer-term use, glycolic acid has also been shown to support collagen in the deeper layers of the skin. Lactic acid is well established for dry, rough skin, and mandelic acid has shown benefit in acne and pigmentation, with some studies suggesting fewer side effects than glycolic acid.

The evidence does have limitations. Many studies are small and short, and a lot of the strongest data comes from in-clinic chemical peels at much higher concentrations than you will find in home skincare. Products also vary widely in strength and acidity, so results from one product cannot simply be applied to another, and there are few direct head-to-head comparisons between the different acids.

One important, well-documented point: AHAs make the skin more sensitive to the sun. Daily sunscreen is non-negotiable while you use them.

Who AHAs suit and who should be cautious

AHAs are excellent for: pigmentation, mild to moderate acne, rough or uneven texture, dull or sun-damaged skin, and oily skin with seborrhoeic dermatitis. For extremely oily skin, a salicylic acid cleanser is usually the better choice, as salicylic acid is oil-soluble and works inside the pore.

Be more cautious if you have:

• Rosacea. I don't recommend a glycolic cleanser. A gentle hydrating cleanser or a PHA-based product is a better fit.

• Eczema, irritated or compromised skin. Glycolic acid penetrates deeply and can aggravate an already inflamed barrier.

• Very young skin just starting with acne. A glycolic cleanser can work well, but it should be paired with a good hydrating, oil-free moisturiser to protect the skin barrier.

• A recent chemical peel or laser treatment. Avoid active products for a few days afterwards.

• Other actives in your routine. Don't overload the skin. If you are introducing glycolic, lactic or mandelic acid products, avoid starting a retinoid at the same time.

Pregnancy. Glycolic, lactic and mandelic acid skincare products are considered safe in pregnancy, because the concentrations are low and most are washed off. The exception I make is leave-on peel-style products. We don't recommend our Repair and Renew Gel in pregnancy, not because we believe it is unsafe, but because some patients leave it on overnight, and I would rather avoid any unnecessary absorption. If it is applied and removed almost straight away, that concern largely falls away. As always, check with your own doctor or midwife.

Why REFORM uses AHAs

We use AHAs across the REFORM range because they are reliable, well understood and work on the concerns we see most in clinic.

Glycolic Acid Foaming Cleanser. An everyday cleanser that we also use for pigmentation, for controlling oil in seborrhoeic dermatitis, and for mild, acne-prone skin.

Repair and Renew Gel. A leave-on glycolic and mandelic acid product that works like a gentle chemical peel. It exfoliates the dead skin cells that block pores, which makes it very good for acne, and it is also excellent for overall photorejuvenation.

Skin Barrier Repair Cream. Here lactic acid works alongside 10% urea, where its main job is hydration rather than exfoliation, for dry, rough skin, eczema and psoriasis.

How to introduce AHAs safely

• Patch testing is an option, but generally not necessary.

• Start slowly. Use your AHA product three days a week and build up by one day a week.

• For very young or sensitive skin, use the glycolic cleanser three times a week, with a gentle cleanser on the days in between.

• For Repair and Renew Gel, start with short contact: apply it for 30 seconds, remove it, then restore the skin barrier with a moisturiser, or with Vitamin B5 Gel and a moisturiser if your skin is very sensitive.

• Always restore the barrier. If you exfoliate the skin, you must repair it. We recommend the REFORM Everyday Moisturiser, adding Vitamin B5 Gel if the barrier is compromised, the skin is very young, or there is eczema, psoriasis or another inflammatory skin condition.

• Wear sunscreen every day.

• If your skin becomes irritated, stop and let it settle before trying again more slowly.

Realistic timelines

AHAs start working almost immediately, and most people notice smoother skin quickly. With acne, the longer you use them, the fewer the breakouts. With pigmentation, results build gradually, and the longer you use them consistently, alongside daily sun protection, the better it gets.

The takeaway

AHAs are in a lot of products for good reason. They smooth the skin, clear away dead skin cells and help with acne, pigmentation and texture, as long as you choose the right acid and protect your skin barrier.

AHAs are one of the best ingredients you can have in your routine: start slowly, repair your skin barrier and wear sunscreen every day.

Relevant REFORM products

• Glycolic Acid Foaming Cleanser for everyday cleansing, pigmentation, oil control and mild acne.

• Repair and Renew Gel (glycolic and mandelic acid) for acne and photorejuvenation.

• Everyday Moisturiser, oil-free, to restore the skin barrier without clogging pores.

• Vitamin B5 Gel for extra barrier support in sensitive, young or inflamed skin.

• Skin Barrier Repair Cream (10% urea and lactic acid) for dry, rough skin, eczema and psoriasis.

• Mineral SPF 30 or SPF Mist for daily sun protection while using AHAs.

Disclosure: Dr Naomi Mackle is the founder of REFORM Skincare, the in-house skincare brand of Adare Dermatology Clinics. REFORM products are recommended where clinically appropriate. This article is for general information and does not replace a personal consultation.