*Disclaimer: I am not a registered dietitian, naturopath, doctor, or other type of healthcare professional. This is simply the product of my own research and opinions, not to be used to replace the recommendations of a registered healthcare professional.
What was once a high school chemistry no-no, is now a holy grail for skincare – yes, I’m talking about skin care acids. Lactic acid, ascorbic acid, citric acid, salicylic acid, glycolic acid, hyaluronic acid, and many others are used to treat a variety of different skin concerns and boast their own unique benefits for the skin. However, despite these great benefits, if the wrong types of acids are used, or even too much of the right ones, then they will further damage the skin rather than improve it. Because there’s so many skin care acids available on the market, I have put together a handy guide in order to help make navigating through the world of skin care acids a little simpler:
Alpha Hydroxy Acids (AHAs)
There are 7 acids commonly used in skincare that fall under the AHA category. These 7 acids include:
1. Citric acid (from citrus fruits)
2. Glycolic acid (from sugar cane)
3. Hydroxycaproic acid (from royal jelly)
4. Hydroxycaprylic acid (from animals)
5. Lactic acid (from lactose or other carbohydrates)
6. Malic acid (from fruits)
7. Tartaric acid (from grapes)
The primary purpose of these acids is to chemically exfoliate; removing the layer of dead skin cells on the surface of the skin to reveal a brighter complexion with improved product absorption and reduced appearance of acne, dark spots and surface wrinkles.
Of these 7 acids, the most common and well researched are glycolic acid and lactic acid. Although these acids belong to the same group, they are different in terms of their strength and size. The difference between glycolic and lactic acid is that glycolic acid has a smaller molecule size, thus making it the stronger of the two acids. The smaller molecules allow glycolic acid to penetrate deeper than lactic acid. Although this may sound like glycolic acid is, by default, the better choice, for those with sensitive skin or no experience using acids, glycolic acid may result in a damaged moisture barrier, severe skin peeling, burning, redness and irritation. Thus, if you have sensitive skin or just starting out with skin care acids, lactic acid may be your best bet.
AHAs are considered safe in cosmetic products at concentrations of 10% or less, at a pH of 3.5 or greater. Stronger concentrations (up to 30%) and a pH as low as 3.0 are safe if applied by a trained professional . If by now your mind has immediately turned to The Ordinary’s AHA 30% + BHA 2% Peeling Solution, I will note that it has a pH of 3.5-3.7; where the pH of AHAs are more important for efficacy (and chance or irritation) than the concentration . Therefore, in the case of The Ordinary, despite the high concentration of AHAs, the pH is still within the safe zone. Additionally, the fact that it is left on for only 10 minutes then washed off further decreases risk of irritation. However, with that being said, this product is still quite strong and, despite the raving reviews, should not be used by those with sensitive skin or inexperienced with acids.
For someone wanting to start out with using acids, they should start with lactic acid at a concentration of 5% once a week for a few weeks, working up to every other day or once a day. Then, once the skin is more used to acids, they can make the switch to a stronger acid (like glycolic acid).
Beta Hydroxy Acids (BHAs)
Like AHAs, BHAs are used as a form of chemical exfoliation. However, unlike AHAs, which include multiple types of acids, the only BHA is salicylic acid (SA). Further, SA is lipid soluble, whereas AHAs are water soluble; meaning that SA is able to permeate into the pores to dissolve sebaceous gland lipids (trapped oil) as well as decrease overall sebum production . SA also boasts anti-inflammatory, anti-microbial and anti-fungal properties, which can be observed at concentrations ranging from 0.5 to 5% . Higher concentrations are typically used for chemical peels administered by trained professionals.
If you’re trying to decide which is right for you, AHAs or BHAs, BHAs are best for sensitive, acne prone skin; whereas AHAs are typically best for someone looking for stronger exfoliation or have age-related skin concerns (like fine lines and wrinkles). If you have multiple skin concerns, both AHAs and BHAs can be used together. Because BHAs are typically gentler and less irritating, SA can be used once or twice a day as part of your daily routine; using a stronger AHA peel once per week. It’s important to make sure that your skin has built up a tolerance to acids, as combining acids increases the risk of over-exfoliation and irritation.
Ascorbic acid is just the chemical name for vitamin C. Our skin normally contains high concentrations of vitamin C, which helps stimulate collagen synthesis and assists in antioxidant protection against UV damage and photoaging. In order for vitamin C to be absorbed topically through the skin, it must be formulated in a stabilized form of ascorbic acid with a pH below 4 . Ascorbic acid can be combined with other antioxidants or used alone at concentrations of 10 to 15% or greater for greatest efficacy. Additionally, ascorbic acid is sensitive to light and air, so look for products with packaging that can be closed tightly and come in dark colours; or made with UV protective materials. Lastly, it’s important to note that penetration is reduced when ascorbic acid is applied topically versus when it is taken orally; meaning that, if you want to reap the most vitamin C rewards, it’s best to opt for foods high in vitamin C (like leafy greens, tomatoes, broccoli, pepper and Brussel sprouts).
Hyaluronic acid is naturally produced by the body, where roughly half of all hyaluronic acid produced is present in the skin . Its purpose is to bind to water to help retain moisture (fun fact: it can attract and retain 1000x its weight in moisture). However, as we age, the amount of hyaluronic acid produced by the body decreases. This reduction in skin hydration results in increased appearance of wrinkles, redness and dermatitis (skin irritation). One of the ways to combat this reduction in hyaluronic acid production is through the topical application of hyaluronic acid. Thus, hyaluronic acid helps moisturize the skin and contributes to the reduction of fine lines and wrinkles (due to improved hydration). This acid can be found in serums, cleansers, toners and moisturizers, can be used daily by all skin types; and combined with other acids.
To conclude, acids can be a very important part of one’s skin routine, however it is important to start small and work your way up (especially with AHAs). Lastly, it’s crucial to use a daily SPF of 30 or higher when incorporating acids into your skincare routine, as skin care acids (especially the exfoliating ones) make skin more sensitive to UV rays.
I hope this helped simplify the complicated world of skin care acids for you. Are there any acids that I missed that you would like me to discuss? If so, let me know in the comments!
 Vidt, D. G., & Bergfeld, W. F. (1997). Cosmetic use of alpha-hydroxy acids. Cleveland Clinic journal of medicine, 64(6), 327–329. https://doi.org/10.3949/ccjm.64.6.327
 Arif T. (2015). Salicylic acid as a peeling agent: a comprehensive review. Clinical, cosmetic and investigational dermatology, 8, 455–461. https://doi.org/10.2147/CCID.S84765
 Pullar, J. M., Carr, A. C., & Vissers, M. (2017). The Roles of Vitamin C in Skin Health. Nutrients, 9(8), 866. https://doi.org/10.3390/nu9080866
 Papakonstantinou, E., Roth, M., & Karakiulakis, G. (2012). Hyaluronic acid: A key molecule in skin aging. Dermato-endocrinology, 4(3), 253–258. https://doi.org/10.4161/derm.21923