Hydroxy acids are chemical exfoliants that are often used in skincare products to treat acne, sun damage, and a variety of other skin conditions. They are mainly split into two groups; Alpha-Hydroxy Acids (AHAs) and Beta-Hydroxy Acids (BHAs). However, more recently, Poly-Hydroxy Acids (PHAs) and AldoBionic Acids (BAs) have been added to the list. So what is AHA? What is BHA? And what is the difference between AHA vs BHA?
What is AHA?
AHAs are water-soluble carboxylic acids made from sugars and fruits that help exfoliate the skin. They do this by removing calcium ions from the bonds that hold skin cells together which weakens the bonds and allows exfoliation to take place .
AHAs are commonly used to treat the signs of sun-damage (photoaging), such as pigmentation, fine lines and wrinkles, enlarged pores, and uneven skin tone. They are generally suitable for all skin types although those with sensitive skin may need to gradually build up a tolerance to AHAs in order to avoid irritation.
Skin Tip: If irritation is a concern for you, opt for AHAs with a higher molecular weight as this means that less of the ingredient is able to penetrate the skin or is slower to penetrate the skin.
Examples of AHAs include (molecular weight):
- Glycolic Acid (72)
- Lactic Acid (90)
- Malic Acid (134)
- Tartaric Acid (150)
- Mandelic Acid (152)
- Citric Acid (192)
Glycolic acid is probably the most well-known and commonly used AHA and is made from the sugar cane plant. It has the smallest molecular weight among AHAs which means that it is better able to penetrate the skin and can be more effective. However, this also means that it has the potential to be more irritating.
- QRX Labs Glycolic Acid Resurfacing Pads
- Glycolix Elite Glycolic Acid Exfoliating Pads
- Paula’s Choice Skin Perfecting 8% AHA Gel Exfoliant
Lactic acid is another well-known AHA that is made from the sugars found in milk (lactose). It is naturally present in our skin as part of the natural moisturizing factors (NMFs) which means that it makes an excellent moisturizer. Lactic acid is generally less irritating than glycolic acid and, due to its moisturizing properties, may be more suitable for those with dry skin.
Malic acid is made from acids found in fruits such as apples. It is less effective than both glycolic acid and lactic acid which is likely due to its larger molecular weight. However, it may enhance the effects of other acids when used in combination .
- Paula’s Choice RESIST Smoothing Treatment
- Juice Beauty Green Apple Peel Full Strength Exfoliating Mask
- Juice Beauty Blemish Clearing Serum
Tartaric acid is a lesser-known AHA that is made from acids found in grapes (and wine!). There is less research to support the effectiveness of tartaric acid, but it is known to have antioxidant properties.
Mandelic acid is made from bitter almond extracts and has a particularly large molecular weight. This means that it is unlikely to cause irritation but probably needs to be combined with other AHAs or BHAs in order to be effective. However, it does have antibacterial and anti-inflammatory properties which may be of benefit to those with acne .
Citric acid is made from citrus fruits and has the largest molecular weight among AHAs. It is often added into skincare products to adjust the pH level closer to the skin’s natural pH (approx. 4.7 – 6). Research regarding the effectiveness of citric acid as a chemical exfoliant has generally looked at concentrations higher than those found within over-the-counter skincare products.
- Exuviance Daily Resurfacing Peel CA10
- NeoStrata Resurface Smoothing Cream
- e.l.f. Cosmetics Daily Face Cleanser
What is BHA?
BHAs are oil-soluble carboxylic acids that can penetrate deeper into the pores to exfoliate and remove dead skin cells and sebum. The most common BHA is salicylic acid but some AHAs, such as malic acid and citric acid, are also BHAs . In addition, derivatives of salicylic acid, such as beta-lipo-hydroxy acid (LHA), are also considered to be BHAs.
BHAs are commonly used to improve the appearance of acne due to their antibacterial and anti-inflammatory properties and their ability to effectively penetrate pores.
Salicylic acid is made from the bark of the willow tree and has a higher molecular weight than a lot of AHAs (138). Like AHAs, salicylic acid can help exfoliate skin and reduce the signs of premature aging. However, due to its ability to reduce oil, it is better suited to oilier skin types in order to avoid over-drying skin.
- Paula’s Choice 2% BHA Gel Exfoliant
- CeraVe Salicylic Acid Cleanser
- The Ordinary 2% Salicylic Acid Masque
Lipohydroxy Acid (LHA)
LHA is a form of salicylic acid that was developed by L’Oreal and is currently only available in their branded skincare products. Like salicylic acid, LHA dissolves in oil and can penetrate the oil glands to reduce oil production.
However, LHA does not penetrate the skin as easily as salicylic acid with research suggesting that only 6% of LHA penetrates the skin vs 58% of salicylic acid. This results in a different type of exfoliation to salicylic acid and AHAs, where LHAs slower penetration causes cell-by-cell exfoliation rather than the broader exfoliation seen with AHAs and other BHAs .
Citric Acid & Malic Acid
Citric acid and malic acid are both classed as AHAs & BHAs due to their chemical structure. Both appear to have antibacterial properties  and citric acid may have an astringent effect, meaning that it can help ‘dry-out’ the skin.
Other Differences Between AHA vs BHA
One key difference between AHAs vs BHAs is how they affect the skin’s photosensitivity.
Photosensitivity refers to the skin’s ability to tolerate UV radiation and plenty of skincare ingredients, as well as some medications, can affect this.
Skincare ingredients can be photosensitizing, meaning that they decrease the skin’s tolerance of UV radiation, or photoprotective, meaning that they increase the skin’s tolerance to UV radiation.
Generally speaking, BHAs are photoprotective whereas AHAs are photosensitizing – although this appears to mainly be the case for glycolic acid.
Which Acids Should You Choose – AHA vs BHA vs Both?
The acid you choose to use will mainly be dependent on your skin type. Both AHAs and BHAs exfoliate the skin, improve the appearance of fine lines and wrinkles, and reduce pigmentation and other signs of sun damage.
However, BHAs are better suited to those with combination or oily, acne-prone skin types and may be too drying for dry and sensitive skin types.
AHAs are generally suitable for all skin types, but those with sensitive skin should opt for higher molecular weight AHAs in order to reduce the risk of irritation.
Those with dry skin may find that lactic acid suits them best due to its excellent ability to hydrate skin.
If you really can’t decide between AHA vs BHA, why not use both? Assuming that you do not have sensitive skin that is!
- The Ordinary AHA + BHA Peeling Solution
- CosRX AHA/BHA Clarifying Treatment Toner
- SkinMedica AHA/BHA Exfoliating Cleanser
The Bottom Line
There isn’t a huge amount of difference between AHA vs BHA as both can achieve similar results. Broadly speaking, AHAs may be better for anti-aging and BHAs may be better for treating acne, however, this is not always the case.
Sometimes acne can be caused by dehydrated skin, in which case BHAs may worsen this and a hydrating AHA, such as lactic acid, may be best.
If you’re not sure which acid will best suit your skin, see your dermatologist for advice.
- Kornhauser, A., Coelho, S. & Hearing, V. (2010). ‘Applications of hydroxyl acids: classification, mechanisms, and photoactivity’, Clin Cosmet Investig Dermatol., 3, 135-142. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3047947/
- Smith, W. (1996). ‘Comparative effectiveness of alpha-hydroxy acids on skin properties’, Int J Cosmet Sci., 18(2), 75-83. Available at: https://www.ncbi.nlm.nih.gov/pubmed/19245467
- Dayal, S., Kalra, K. & Priyadarshini, S. (2019). ‘Comparative study of efficacy and safety of 45% mandelic acid versus 30% salicylic acid peels in mild-to-moderate acne vulgaris’, J Cosmer Dermatol., 19(2), 393 – 399. Available at: https://onlinelibrary.wiley.com/doi/abs/10.1111/jocd.13168
- Zeichner, J. (2016). ‘The use of lipohydroxy acid in skin care and acne treatment’, J Clin Aesthet Dermatol., 9(11), 40-43. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5300717/
- Tang, S. & Yang, J. (2018). ‘Dual effects of alpha-hydroxy acids on the skin’, Molecules, 23(4), 863. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6017965/