"Acids" in skincare cover two very different jobs: chemical exfoliants (glycolic, lactic, salicylic) that dissolve the bonds between dead cells to smooth and unclog, and functional acids (hyaluronic, azelaic, tranexamic) that hydrate, calm or fade pigment without exfoliating at all. Choosing the right one starts with knowing which job you need done.
The word covers a lot of ground. Alpha-hydroxy acids (glycolic, lactic, mandelic) are water-soluble and work on the surface to smooth texture and brighten. Beta-hydroxy acid (salicylic) is oil-soluble, so it gets into pores — the reason it suits oily, acne-prone skin. Polyhydroxy acids are larger, slower and gentler, a good entry point for sensitive skin.
Then there are acids that are not exfoliants at all: hyaluronic and polyglutamic are humectants that hold water; azelaic calms and evens tone; tranexamic targets pigment; hypochlorous is an antimicrobial. Grouping them by the chemical suffix hides how differently they behave — so we sort them by what they do below.
Every acid we cover, with what it does and the concerns it is most often used for. Each name links to its full glossary entry.
| Ingredient | What it is | Most used for |
|---|---|---|
| Hyaluronic Acid | A glycosaminoglycan naturally present throughout the body, holding up to 1000x its weight in water. | Dryness, Aging |
| Glycolic Acid | The smallest AHA molecule — 76 daltons — allowing the deepest penetration and most potent exfoliation. | Texture, Dullness, Pigmentation |
| Lactic Acid | The gentlest commonly used AHA — larger molecular weight than glycolic means shallower penetration and less irritation. | Texture, Dullness, Dryness |
| Mandelic Acid | The largest commonly used AHA — 152 daltons — giving the slowest and most superficial penetration. | Texture, Pigmentation, Acne |
| Salicylic Acid | The only BHA widely used in skincare and the gold standard for acne and congested skin. | Acne, Oiliness, Texture |
| PHAs | Next-generation exfoliants larger than AHAs — the gentlest chemical exfoliants available. | Texture, Dullness, Redness |
| Azelaic Acid | A dicarboxylic acid from grains with a uniquely versatile clinical profile: antibacterial (kills C. | Acne, Redness, Pigmentation |
| Tranexamic Acid | Originally a pharmaceutical antifibrinolytic, TXA is now one of the most effective topical ingredients for hyperpigmentation — including melasma and PIH. | Pigmentation |
| Kojic Acid | A chelating agent derived from fungal fermentation (sake, soy sauce). | Pigmentation, Dullness |
| Benzoyl Peroxide | One of the most effective OTC acne treatments. | Acne |
| Hypochlorous Acid | A mild antimicrobial molecule the immune system makes naturally — white blood cells generate it to neutralise bacteria and calm inflammation. | Redness, Acne |
| Polyglutamic Acid | A water-soluble biopolymer of chained glutamic-acid units, produced by bacterial fermentation (classically natto). | Dryness |
Across the catalogue, the acids here are most often used for these concerns — each links to its evidence-led concern hub with a full routine:
Texture (5), Pigmentation (5), Acne (5), Dullness (4), Dryness (3), Redness (3), Aging (1), Oiliness (1).
These commonly pair well with: Niacinamide, Hyaluronic Acid, Ceramides, Vitamin C, Panthenol, Azelaic Acid. Pairing is about getting more from a routine without adding irritation — humectants, barrier lipids and niacinamide are frequent partners here.
Commonly flagged to avoid combining directly: Retinol, Retinaldehyde, Salicylic Acid, Glycolic Acid, Benzoyl Peroxide, Vitamin C. These conflicts are usually about irritation or destabilisation, not danger — often solved by using them at different times of day.
AHAs (like glycolic and lactic acid) are water-soluble and work on the skin surface to smooth texture and brighten tone. BHA (salicylic acid) is oil-soluble, so it penetrates into pores to clear congestion — which is why it suits oily and acne-prone skin. Many routines use both, on different days.
Polyhydroxy acids (PHAs) and mandelic acid have larger molecules that penetrate more slowly, causing less irritation than glycolic acid. Lactic acid is a good middle option that also hydrates. Start with one, once or twice a week, and build up as your skin tolerates it.
You can, but stacking strong exfoliating acids in one routine raises the risk of irritation and a damaged barrier. A safer approach is to use one exfoliant at a time and alternate nights. Functional acids like hyaluronic or azelaic acid are not exfoliants and layer comfortably with almost anything.
Yes. Exfoliating acids remove dead surface cells and can make skin temporarily more sensitive to UV, and they undo their own benefits if you then let sun damage accumulate. Daily broad-spectrum sunscreen is non-negotiable whenever you use AHAs or BHA.
Browse the rest of the ingredient library: Retinoids, Vitamins, Peptides — or see the full ingredient categories index.
Written and reviewed by JoAnn, editor of Skin Stacker — see our methodology and editorial standards.
Reviewed / last updated: 2026-07-17. For informational purposes only — not a substitute for medical advice.