Acids in skincare: what they are, how they work, and which one is right for you

A beginner-friendly guide. Last updated May 2026

Walk into any skincare aisle and you'll see acids listed on nearly every bottle. Glycolic acid. Salicylic acid. Hyaluronic acid. But what do they actually do, and should you be worried? Here's everything you need to know, no chemistry degree required.

Not all acids are the same

The word "acid" sounds harsh, but in skincare it usually refers to gentle chemical compounds that help your skin shed dead cells and stay healthy. There's one important exception to know right away: hyaluronic acid is not an exfoliating acid at all. Despite the name, it's a hydrating ingredient that draws moisture into the skin.

The main category of skincare acids are exfoliating acids, which dissolve the bonds between dead skin cells, helping fresh skin emerge. They fall into three families based on molecular size and how deep they work: AHAs, BHAs, and PHAs. The key difference lies in molecular size and oil solubility; smaller molecules penetrate deeper, and oil-soluble acids can work inside pores, while water-soluble acids work on the surface.

The three families: AHA, BHA, and PHA

Alpha hydroxy acids, or AHAs, are typically water-soluble and vary in molecular size depending on the specific acid. In general, they're best for dry, dull skin types. They exfoliate the surface of the skin and also act as humectants, meaning they help attract and hold moisture.

BHAs are oil-soluble, so they can bind to sebum in the pores and penetrate deeper into the skin than AHAs. BHAs also have anti-inflammatory benefits, making them particularly useful if you struggle with clogged pores and acne.

PHAs are the newest generation of exfoliating acids. With much larger molecules than AHAs or BHAs, they work exclusively at the surface level. No deep penetration means minimal irritation potential. PHAs also function as humectants, attracting moisture while they exfoliate, making them the gentlest possible introduction to acid exfoliation.

Common acids you'll see on labels

Glycolic acid (AHA)

Glycolic acid is powerful because it's the AHA with the smallest molecules, usually naturally derived from sugar cane. It works to exfoliate at deeper levels in the skin and help even out skin tone. Because of its potency, it can increase sun sensitivity, so wearing sunscreen in the morning is essential when using it.

Lactic acid (AHA)

Lactic acid has larger molecules than glycolic acid, so it works more gently on the skin's surface. It's naturally occurring — lactic acid is found in sour milk. It's a good starting point for AHA beginners or anyone who finds glycolic acid too strong.

Salicylic acid (BHA)

Salicylic acid, derived from willow bark, is a BHA known for its effectiveness in skincare. Functioning as a mild exfoliator, it promotes surface skin cell turnover and helps keep pores clear by preventing the accumulation of debris that often leads to blackheads and whiteheads. It's a staple ingredient in acne products. Worth noting: salicylic acid can be absorbed through the skin, so it's important not to use it in large amounts, and its use during pregnancy is controversial — expectant mothers should consult their doctors before using it.

Gluconolactone (PHA)

Research shows gluconolactone provides the same smoothing and clarifying benefits as glycolic acid, but without the stinging, burning, or increased sun sensitivity. It's an excellent option for anyone who has found AHAs or BHAs too irritating.

Hyaluronic acid (not an exfoliant)

Despite sharing the word "acid," hyaluronic acid doesn't exfoliate at all. It's a humectant, meaning it draws moisture from the environment into the skin. One of its most impressive qualities is its ability to hold up to 1,000 times its weight in water, leaving skin feeling full and bouncy. It pairs well with nearly every other skincare ingredient.

Resources

1. Măgerușan ȘE, Hancu G, Rusu A. A Comprehensive Bibliographic Review Concerning the Efficacy of Organic Acids for Chemical Peels Treating Acne Vulgaris. Molecules. 2023 Oct 22;28(20):7219. doi: 10.3390/molecules28207219. PMID: 37894698; PMCID: PMC10608815.

   
   

2. Kornhauser A, Wei RR, Yamaguchi Y, Coelho SG, Kaidbey K, Barton C, Takahashi K, Beer JZ, Miller SA, Hearing VJ. The effects of topically applied glycolic acid and salicylic acid on ultraviolet radiation-induced erythema, DNA damage and sunburn cell formation in human skin. J Dermatol Sci. 2009 Jul;55(1):10-7. doi: 10.1016/j.jdermsci.2009.03.011. Epub 2009 May 2. PMID: 19411163; PMCID: PMC2791365.
   

3. Moghimipour E. Hydroxy Acids, the Most Widely Used Anti-aging Agents. Jundishapur J Nat Pharm Prod. 2012 Winter;7(1):9-10. Epub 2012 Jan 4. PMID: 24624144; PMCID: PMC3941867.
   

4. Almeman AA. Evaluating the Efficacy and Safety of Alpha-Hydroxy Acids in Dermatological Practice: A Comprehensive Clinical and Legal Review. Clin Cosmet Investig Dermatol. 2024 Jul 16;17:1661-1685. doi: 10.2147/CCID.S453243. Erratum in: Clin Cosmet Investig Dermatol. 2024 Aug 30;17:1973-1974. doi: 10.2147/CCID.S493491. PMID: 39050562; PMCID: PMC11268769.

   
   

5. Karwal K, Mukovozov I. Topical AHA in Dermatology: Formulations, Mechanisms of Action, Efficacy, and Future Perspectives. Cosmetics. 2023; 10(5):131. https://doi.org/10.3390/cosmetics10050131

   
   
   
   

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