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What are alpha-hydroxy acids?

Alpha-hydroxy acids are chemical compounds that are sometimes added to skincare products and in-office facial treatments.  What are alpha-hydroxy acids, what do they do, and what are their associated benefits and side effects?

What are alpha-hydroxy acids?

Alpha-hydroxy acids (AHAs) are molecules that have a relatively acidic pH and a specific chemical structure.  They are sometimes present in over-the-counter skin care products and serums due to their ability to encourage exfoliation of dead skin cells on the very top layer of the skin, called the epidermis.1  

AHAs are also used in higher concentrations in some facial treatments and procedures available at dermatology and cosmetic clinics, including superficial chemical peels.2  Chemical peels use chemical exfoliants to resurface the skin for cosmetic and medical purposes, and superficial refers to the depth of the peel; superficial chemical peels only target the epidermis rather than the deeper layers of skin.3

Chemical exfoliation using AHAs is thought to help brighten skin by removing dead skin cells on the epidermis that may be associated with the appearance of dull skin.  AHAs are also thought to help reduce signs of photoaging; one study found that using a lotion containing 25% glycolic, lactic, or citric acid was associated with increased skin thickness and elasticity, as well as increased skin collagen.4 

Some research also suggests that superficial chemical peels, such as those using AHAs, may help reduce the appearance of post-inflammatory hyperpigmentation, acne, and acne scarring.3,5,6  More research is needed to determine the potential benefits of AHAs for skin health and appearance.

There are a variety of AHAs that are used for cosmetic and clinical purposes.  Glycolic acid, which is derived from sugar cane, is commonly used in skincare products and peels because it penetrates the skin easily and it is relatively well-studied compared to other AHAs.7.8  Lactic acid, which comes from fermented milk, is also well-studied, and some research suggests that it is more gentle than glycolic acid, and it may even have hydrating and moisturizing properties.9 

Other AHAs include citric acid from citrus fruits, mandelic acid from bitter almonds, malic acid from apples, and tartaric acid from fermented grapes.7  Citric acid, in particular, is commonly used in a variety of products to lower its overall pH, or make it more acidic.10  More research is needed to determine the potential benefits of these less-studied AHAs.

How do alpha-hydroxy acids work?

Although the exact mechanism of how AHAs work is not fully known, part of their therapeutic effect is likely due to the ability to induce desquamation, which is a term for exfoliating dead skin cells from the epidermis.  When AHAs are applied to the skin, they interfere with the bonds between the skin cells, which weakens the dead skin’s ability to adhere to the epidermis.7  As a result, these dead skin cells come off more easily. 

There is also some evidence to suggest that AHAs may increase skin thickness and collagen production; however, more research is needed to validate these claims.7

What are the side effects?

Some common side effects associated with AHAs are skin irritation, dryness, and a burning sensation.  More severe side effects may include blistering or crusting of the skin.7  The severity of these side effects depends on the dose; since the concentration of AHAs used in chemical peels at clinics is generally much higher, they may be associated with a more severe side effect profile than over-the-counter AHA products.7 

Using AHAs may also be associated with increased sun sensitivity; one study found that participants who used glycolic acid had a greater sensitivity to UV light than those who used a placebo.11  When using topical AHAs, it is especially important to limit sun exposure and use broad-spectrum sunscreens that protect against both UVA and UVB radiation.

Seek medical help if you experience any side effects that you are concerned about when using topical AHAs.  Additionally, seek medical help immediately if you experience signs of an allergic reaction after using topical AHAs, such as chest tightness, hives, or swelling of the face, mouth, and throat.

There is also a potential for AHAs to interact with other skincare products or oral medications; for this reason, it is important to tell your healthcare provider about any medications, vitamins, and supplements that you may be using.

This article is not medical advice, and it is not intended to prescribe, diagnose, or promote specific treatments for any condition.  Consult your doctor, dermatologist, or other qualified healthcare provider for your unique skin needs.

Image by Woon Kuongchin from Pixabay 


  1. Kornhauser, A., Coelho, S.G., Hearing, V.J. (2010). Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol 3: 135-142. Doi: 10.2147/CCID.S9042
  2. Tang, S., Yang, J. (2018, April). Dual effects of alpha-hydroxy acids on the skin. Molecules 23(4): 863. Doi: 10.3390/molecules23040863
  3. O’Connor, A.A., Lowe, P.M., Sumac, S., Lim, A.C., (2017, October). Chemical peels: a review of current practice. Australasian Journal of Dermatology 59(3): 171-181. Doi: 10.1111/ajd.12715
  4. Ditre, C.M., Griffin, T.D., Murphy, G.F., et al (1996, February). Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study. J Am Acad Dermatol 34(2 Pt 1): 187-195. Doi: 10.1016/s0190-9622(96)80110-1.
  5. Castillo, D.E., Keri, J.E. (2018, July). Chemical peels in the treatment of acne: patient selection and perspectives. Clinical, Cosmetic, and Investigational Dermatology 11. Doi: 10.2147/CCID.S137788.
  6. Usuki, A., Ohashi, A., Sato, H., et al (2003). The inhibitory effect of glycolic acid and lactic acid on melanin synthesis in melanoma cells. Exp Dermatol 12(Suppl 2): 43-50. Doi: 10.1034/j.1600-0625.12.s2.7.x
  7. Babilas, P., Knie, U., Abels, C. (2012, May 11). Cosmetic and dermatologic use of alpha hydroxy acids. JDDG: Journal der Deutschen Dermatologischen Gesellschaft 10(7): 488-491. Doi: 10.1111/j.1610-0387.2012.07939.x
  8. Sharad, J. (2013, November). Glycolic acid peel therapy – a current review. Clin Cosmet Investig Dermatol 6: 281-288. Doi: 10.2147/CCID.S34029
  9. Abd Alsaheb, R.A., Aladdin, A., Othman, N.Z., et al (2015). Lactic acid applications in pharmaceutical and cosmeceutical industries. Journal of Chemical and Pharmaceutical Research 7(10): 729-735. Accessed online from
  10. Soccol, C.R., Vandenberghe, L.P.S., Rodrigues, C., Pandey, A. (2006). New perspectives for citric acid production and application. Biotechnol 44(2): 141-149. Accessed online from
  11. Kaidbey, K., Sutherland, B., Bennett, P., et al (2003, March). Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatology, Photoimmunology & Photomedicine 19(1): 21-27. Doi: 10.1034/j.1600-0781.2003.00013.x



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