Glass & Dew
AboutEditorial policyDisclaimerPrivacyContact

AHA (alpha hydroxy acids)

aka Alpha hydroxy acids, AHA, Glycolic Acid, Lactic Acid, Mandelic Acid, Citric Acid, Malic Acid, Tartaric Acid

The short answer

AHAs like glycolic and lactic acid loosen the bonds between dead cells on the surface of your skin, so it looks smoother and more even. They can make skin more sensitive to the sun for about a week after you stop, so daily SPF50+ is non-negotiable.

Known for
Water-soluble acids that loosen dead surface cells for smoother, brighter-looking skin.
Helps with
Rough or bumpy textureDullnessUneven-looking toneSurface fine lines
Evidence
moderate

Updated 6 Oct 2026 · Sources

Check first

Caution: Sun sensitivity lasts a week after stoppingCaution: Can stingCaution: Over-exfoliationCaution: Darker skin: go gently
  • Your skin is sunburnt, broken or irritated; the AAD advises against exfoliating over wounds or sunburn.
  • You're using a prescription retinoid or retinol and haven't planned alternate nights.
  • You have darker skin that marks easily; aggressive exfoliation can leave dark spots, so start with a low-strength or lactic acid product.
  • You're already using another exfoliating acid in the same routine.

What it goes with

Pairs well

  • Hyaluronic acidAdds water-based hydration after exfoliation; no clash is known.
  • CeramidesA barrier-supporting moisturiser straight after exfoliating fits the AAD's 'moisturise immediately' advice.
  • PanthenolA soothing humectant that helps skin feel comfortable after acids.
  • NiacinamideNo source shows the two cancel each other out. If the combination stings, use them at different times.
  • SPF50+ sunscreenFDA-sponsored research found AHAs raise UV sensitivity, so sunscreen is part of using them.

Keep apart

  • Avoid: RetinolThe AAD advises not exfoliating while using retinol or prescription retinoids. Alternate nights instead.
  • Avoid: BHA (salicylic acid)One exfoliant per routine keeps irritation in check; no study tested layering them.
  • Avoid: Vitamin CBoth are low-pH; together they stack irritation. Vitamin C in the morning, acids at night.
  • Avoid: Tranexamic acidA clinic guide advises not applying TXA at the same time as strong AHA or BHA exfoliants or at-home peels.
  • Avoid: NiacinamideNo opened source shows either ingredient is inactivated by the other; it's about comfort, not chemistry.

How it works

AHAs are small, water-soluble acids with a hydroxyl group on the alpha carbon. Glycolic acid comes from sugar cane, lactic acid from milk, citric acid from citrus, malic acid from apples and tartaric acid from grapes [2][4]. They loosen the connections between dead cells on the skin's surface so those cells shed more evenly, which is what makes skin look smoother and brighter [1][3].

How strong an AHA product is depends on more than the percentage: concentration, pH, contact time and the amount of 'free acid' all matter [3]. At a lower pH more of the acid is in its free, uncharged form, which penetrates more easily, so a lower pH means more exfoliation and more chance of irritation [7]. The main international benchmark, from the US Cosmetic Ingredient Review panel, is 10% or less at pH 3.5 or above for consumer products; professional peels use 20% to 70% [1][4].

Reviews describe AHA use for sun-damaged skin, breakouts and uneven pigmentation [2], and lactic acid is described as less irritating than glycolic acid [3]. Lab and small biopsy studies found glycolic acid increased hyaluronic acid and collagen-related activity in skin [2]; that is a research finding, not a product promise.

The most important fact is about the sun. In FDA-sponsored studies, four weeks of AHA use raised UV-induced skin reddening by 18% and roughly doubled UV damage to skin cells; one week after stopping, sensitivity was back to normal [1]. One study also found glycolic acid pretreatment increased UV tanning [2], so any brightening goal depends on sunscreen.

Mandelic acid is often marketed as a gentler AHA for sensitive or darker skin because it is a larger molecule. We couldn't find a published clinical study backing that, so count it as unconfirmed.

How to use it

  • Start two or three nights a week and build up only if your skin stays comfortable.
  • Apply to clean, dry skin at night, then moisturise straight away [5].
  • For leave-on products, stay at or under 10% with a pH of 3.5 or above; anything stronger is a peel, so follow the directions exactly [1][4].
  • New to acids? Lactic acid is described as less irritating than glycolic [3].
  • Wear SPF50+ every day while using AHAs and for a week after you stop [1][11].
  • A little tingling can be normal; burning, swelling or a rash means stop [1][6].
  • Try a new product on your inner arm twice a day for 7 to 10 days first [6].

FAQ

AHAs are water-soluble and work on the skin's surface; salicylic acid (BHA) is oil-soluble, mixes with skin oil and works inside pores, so it suits oilier skin [2].

Products with aha (alpha hydroxy acids)

Each links to Australian stockists, with the price range across shops.

Sources

General information only, not medical advice.