Alpha Hydroxy Acids (AHAs) vs. Beta Hydroxy Acids (BHAs)
AHAs and BHAs are Both Hydroxy Acids Used to Treat Acne, but Differ in How They Affect the Skin
Alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs) are acids used to treat a variety of skin diseases, including acne. Both AHAs and BHAs act similarly to exfoliate the skin but possess different chemical properties that affect how they act on and in the skin.
It appears that both AHAs and BHAs clear acne to a similar degree. However, since neither will completely clear acne on their own, both AHAs and BHAs are often combined with other acne medications.
Examples of widely-used AHAs: Glycolic acid, lactic acid, mandelic acid
Examples of widely-used BHAs: Salicylic acid is the only widely-used BHA
- Introduction to AHA and BHA
- Differences Between AHA and BHA
- Similarities Between AHAs and BHAs
- Side Effects of AHAs and BHAs
- Comparing the Effectiveness of AHAs and BHAs
Introduction to AHA and BHA
Hydroxy acids are a group of acids used to treat a variety of skin conditions, including acne. There are two main classes of hydroxy acids:
- Alpha hydroxy acids (AHAs)
- Beta hydroxy acids (BHAs)
The main AHA used to treat acne is glycolic acid, while by far the most common BHA used to treat acne is salicylic acid. Most studies investigating AHAs and BHAs focus on glycolic acid or salicylic acid. Both alpha and beta hydroxy acids work mainly by exfoliating the top layer of skin, which helps to clear pores and prevent acne, but they achieve this by different mechanisms.1,2
Differences Between AHA and BHA
There are several differences between AHAs and BHAs, which determine how they work to treat acne and affect the skin in general.
How they work to treat acne
- Solubility: Solubility is a scientific term to describe the ability of a substance to dissolve in another substance.
- AHA: Alpha hydroxy acids are water soluble, which means they dissolve well in water. This is relevant to acne because water-soluble solutions cannot penetrate into oil-filled areas like the inside of a pore, where acne begins, so they can only act on the surface of the skin.
- BHA: Beta hydroxy acids are oil soluble, which means they dissolve well in oil. This is relevant to acne because oil-soluble solutions can enter into the oil-filled pore and act to exfoliate the skin from within the pore.
- How they exfoliate: In order to stimulate peeling of the uppermost layer of the skin, all hydroxy acids must interact with skin proteins that hold skin cells together
- AHA: Alpha hydroxy acids break down the sticky protein, keratin. Keratin is an important protein that acts like glue to stick dead skin cells together. By breaking down keratin, AHAs help "pull" skin cells apart and stimulate peeling of the uppermost layer of skin.
- BHA: Beta hydroxy acids act on proteins called desmosomes. Desmosomes stick out of skin cells and act to connect one cell to the next. BHAs break down desmosomes, which helps pull skin cells apart, stimulating peeling of the outermost layer of skin.
- Anti-inflammatory properties: Inflammation is a major factor in acne, and is present in all stages of acne development. In fact, inflammation is thought to be the trigger that causes acne to develop.
- AHA: The science is not yet conclusive on whether alpha hydroxy acids have anti-inflammatory properties
- BHA: Beta hydroxy acids are anti-inflammatory acids, meaning that they can decrease inflammation in acne lesions, which could have some effect on the clearing and prevention of acne lesions
- Over-the-counter concentrations: Both AHAs and BHAs are available in concentrations up to 70%. However, only lower concentrations are safe for use at home in over-the-counter products.
- AHA: Alpha hydroxy acids are available in over-the-counter in concentrations ranging from 1 - 10%. Products containing a concentration greater than 10% should only be administered by a skin care professional like a nurse or esthetician.
- BHA: Beta hydroxy acids are available in over-the-counter products in concentrations ranging from 0.5% to 2%. Products containing a concentration greater than 2% should only be administered by a skin care professional.
Effects on skin in general
- Anti-aging: The skin contains a matrix of proteins that help support its structure and shape. Collagen is an important protein in this matrix that helps to support the skin. If there is a decrease in collagen, which happens naturally during aging, wrinkles form.
- AHA: Alpha hydroxy acids can increase the production of collagen in the skin, and therefore decrease the signs of aging
- BHA: Beta hydroxy acids show no anti-aging effects
- Sun sensitivity: Since hydroxy acids work by peeling off the top layer of skin, it is thought that they make the skin more sensitive to the sun's rays. This is important because a sunburn can cause acne in the days and weeks following over-exposure to the sun as the skin repairs itself. The U.S. Food and Drug Administration (FDA) recommends employing some form of sun protection when using either an AHA or BHA. However, the research on sun sensitivity and AHAs differs from that on BHAs.
- AHA: Research has clearly shown that AHAs increase sun sensitivity, and therefore sun protection should always be worn when using an AHA
- BHA: Although BHAs work to thin the top layer of skin, research has found that BHAs do not increase sensitivity to the sun. Despite this finding, the FDA still recommends that people using BHAs practice some form of sun protection just in case peeling of the skin results in sun sensitivity.1,3-6
Similarities Between AHAs and BHAs
There are several similarities between AHAs and BHAs in how they work to clear acne.
- Exfoliation: Both AHAs and BHAs impact acne by exfoliating the top layer of skin, which helps to unclog clogged pores and prevent the formation of new ones
- Skin penetration: Both AHAs and BHAs affect only the uppermost layer of the skin, known as the stratum corneum. Neither AHAs nor BHAs have the ability to penetrate into deeper layers of the skin.
- Reducing sebum: Sebum (skin oil) is normally produced by the skin to keep it healthy and hydrated. Acne-prone individuals often produce more sebum than non-acne-prone individuals, and this sebum accumulates in clogged pores and causes acne. Both AHAs and BHAs work to decrease sebum.4-6
- Antibacterial properties: One factor involved in the development of acne is the bacteria called P. acnes, which grows inside clogged pores and can make acne worse by increasing inflammation and triggering the development of pus. Both AHAs and BHAs have antibacterial properties, which can help clear P. acnes from clogged pores and help prevent the worsening of acne.
- Reducing hyperpigmentation: When an acne lesion heals, it can leave behind red/dark marks on the skin. These marks are called post-inflammatory hyperpigmentation, or hyperpigmentation for short. Both AHAs and BHAs can decrease hyperpigmentation by stimulating the growth of new skin cells, which replace the old, discolored skin cells and improve the appearance of the skin.
Side Effects of AHAs and BHAs
The side effects of AHAs and BHAs are similar and generally mild. These side effects include:
- Skin irritation: Both AHAs and BHAs can cause mild to moderate skin irritation
- Stinging and/or burning sensations: Both AHAs and BHAs can cause mild to moderate stinging or burning sensations
- Scaling and/or peeling of skin: Research has found that 25% of AHA-treated patients and 17 - 25% of BHA-treated patients report scaling and/or peeling of the skin. The number of people experiencing side effects will likely decrease with lower concentrations.
- Dryness and/or crusting of skin: Research has found that 20% of AHA-treated patients and 20 - 32% of BHA-treated patients report dryness and/or crusting of the skin. The number of people experiencing side effects will likely decrease with lower concentrations.
- Redness: Research has found that 60% of AHA-treated patients and 8.8 - 50% of BHA-treated patients reported redness of the skin. The number of people experiencing side effects will likely decrease with lower concentrations.
- Photosensitivity: Research has found that AHAs cause sun sensitivity, while BHAs do not. However, because both AHAs and BHAs promote peeling of the top layer of skin, the FDA recommends that people using AHAs and BHAs always wear some form of sun protection during the entire treatment course.2,7
Comparing the Effectiveness of AHAs and BHAs
Scientists have performed three studies directly comparing the effectiveness of AHAs vs. BHAs on acne.
Expand to read details of these three studies
A 2008 study published in Dermatologic Surgery compared the efficacy of a 30% glycolic acid peel with that of a 30% salicylic acid peel. To perform this study, the researchers conducted a split-face treatment, meaning that they applied the glycolic acid peel to half of the face, and the salicylic acid peel to the other half of the face, in 20 patients. Each patient underwent a total of six peels, performed every two weeks. The researchers found that two months following treatment, 75% of the glycolic acid - treated skin and 81% of the salicylic acid - treated skin showed good or fair improvement of mild to moderate acne. Although the salicylic acid peel performed slightly better, more patients considered the glycolic acid peel to display a better efficacy, meaning that they perceived that the glycolic acid peel worked better than the salicylic acid peel.3
A 2004 study published in the International Journal of Cosmetic Science compared the efficacy of a 2% lactic acid (a type of AHA) treatment with that of a 2% salicylic acid treatment on acne. To perform this study, the researchers had 90 participants apply the acid products twice daily over the course of 12 weeks. The researchers found that lactic acid was slightly more effective than salicylic acid at reducing comedones.8
A 2011 study published in the Journal of the European Academy of Dermatology and Venereology compared several independent AHA and BHA studies in order to draw conclusions regarding the ability of glycolic acid and salicylic acid to clear acne. This research found that 30% glycolic acid peels resulted in 75% of patients reporting good improvement of acne, while a 30% salicylic acid peel resulted in a 75% reduction of lesions. Although these two measurements cannot be equally compared, as one measures patient opinion and the other measures reduction of acne lesions, it is clear from these results that both 30% glycolic acid and 30% salicylic acid are effective, to some extent at clearing acne.1
Using this data, we can see that AHAs and BHAs appear to work to a similar degree. However, more research is needed to compare different concentrations of AHAs and BHAs before definitive conclusions can be made regarding which is better to treat acne.
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- Dréno, B. et al. Efficacy of superficial chemical peels in active acne management - What can we learn from the literature today? Evidence-based recommendations. J Eur Acad Dermatol Venereol 25, 695 - 704 (2011).
- Kornhauser, A., Coelho, S. G. & Hearing, V. J. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol 3, 135 - 142 (2010).
- Kessler, E., Flanagan, K., Chia, C., Rogers, C. & Glaser, D. A. Comparison of α- and β-hydroxy acid chemical peels in the treatment of mild to moderately severe facial acne vulgaris. Dermatol Surg 34, 45 - 51 (2008).
- Yu, R. J. & Van Scott, E. J. Alpha-hydroxyacids and carboxylic acids. J Cosmet Dermatol 3, 76 - 87 (2004).
- Arif, T. Salicylic acid as a peeling agent: a comprehensive review. Clin Cosmet Investig Dermatol 8, 455 - 461 (2015).
- Decker, A. & Graber, E. M. Over-the-counter acne treatments: A review. J Clin Aesthet Dermatol 5, 32 - 40 (2012).
- Babilas, P., Knie, U. & Abels, C. Cosmetic and dermatologic use of alpha hydroxy acids. J Ger Soc Dermatol 10, 488 - 491 (2012).
- Scherdin, U. et al. In vivo assessment of the efficacy of an innovative face care system in subjects with mild acne vulgaris. Int J Cosmet Sci 26, 221 - 229 (2004).