Exfoliation has long been the secret to glowing, healthy-looking skin. But you don’t need a harsh, gritty scrub to get the job done. Alpha- and beta-hydroxy acids are the best way to remove dead skin cells, using chemical (not physical) methods.
Also known as AHAs and BHAs, they’re the two most common families of exfoliating acids that you’ll see in skincare products—and they’re often found together.
So how do they actually work? Which type is best for your skin? And can you get better results if you use both of them?
If you’ve been asking these questions, this tutorial is for you. You will learn the difference between AHAs and BHAs, how to choose the right one, and whether it’s beneficial to incorporate both types in one routine. I’m also sharing some of my favourite AHA and BHA products that I always recommend.
What Is AHA?
AHA stands for alpha-hydroxy acid—a type of naturally-occurring acid that is present in many foods and milk sugars.
AHAs work by peeling away dead skin cells, revealing the fresh new skin cells underneath. They do so by weakening the bonds between the cells (corneocytes) in the uppermost layer of our skin, causing them to detach and flake off.
But how exactly do they do that? Several studies suggest that it is by overloading the cells with calcium—which leads to cell death—that AHAs are able to disrupt these adhesions.
Researchers have found that AHAs create acidic conditions within the cells and cell adhesions. This allows calcium ions to flow in, to the point where they overload the cells, disrupt cell adhesions, and trigger cell death (apoptosis).
Types of AHAs
These are the different types of AHAs that you will see in skincare products:
- Glycolic acid: The most common AHA, derived from sugarcane. It is also the strongest, due to its small molecule size, but that makes it the most irritating, too.
- Lactic acid: The second most common AHA, derived from milk. It’s a gentler alternative to glycolic acid, and can be appropriate for sensitive skin.
- Mandelic acid: A mild AHA derived from bitter almonds. As it is weaker than lactic acid, it’s usually combined with other acids. However, some experts such as Dr. Loren Pickart believe it can be neurotoxic.
- Malic acid: A mild AHA derived from apples. Like mandelic acid, it won’t do enough on its own, so you’ll typically see it in combination with stronger AHAs.
- Tartaric acid: A weak AHA derived from grapes. Instead of acting as an exfoliant, it is more often used to stabilize other acids’ pH levels.
- Citric acid: A weak AHA derived from citrus fruits. It is similar to tartaric acid in that it regulates pH. It is also used as a preservative.
- Phytic acid: A weak AHA derived from rice, seeds and grains. It is commonly used as an antioxidant.
What Is BHA?
BHA stands for beta-hydroxy acid, a type of acid that is derived from willow tree bark, wintergreen leaves or sweet birch bark.
Just like AHAs, BHAs exfoliate your skin surface by decreasing the adhesion of dead skin cells (corneocytes), causing them to loosen and detach. However, this is achieved by dissolving intercellular lipids, rather than initiating cell death.
Since BHAs are oil-soluble, they penetrate below the skin surface as well, exfoliating inside the pores. This allows oil to flow out more freely, preventing the build-up of dead skin and sebum that leads to clogged and stretched-out pores.
Types of BHAs
The main BHA exfoliants you’ll see in skincare products are:
- Salicylic acid: The most common BHA, and also the strongest. However, it is not as irritating as glycolic acid (the strongest AHA) because of its large molecule size and anti-inflammatory nature.
- Betaine salicylate: A BHA comprised of salicylic acid and betaine (a hydrating amino acid derived from sugar beets). It’s a gentler alternative to salicylic acid, and according to data from the manufacturer, is equally effective. (A 4% concentration of betaine salicylate is said to be equivalent to 2% salicylic acid.)
- Salix alba or willow bark extract: A natural BHA derived from willow bark. The salicin content converts into salicylic acid, but it is much weaker (so it won’t give you as dramatic results).
How AHA and BHA Are Similar
You may have heard that AHAs are best for exfoliating, brightening and anti-aging, while BHAs are only suitable for people with acne.
Fortunately, that isn’t true. These are all the benefits that both AHAs and BHAs have in common:
- Exfoliating and smoothing: AHAs and BHAs are both effective at removing surface dead skin cells and creating a soft, smooth texture.
- Brightening: Both AHAs and BHAs have been found to reduce the thickness of the stratum corneum, the top layer of skin consisting of dead skin cells. This allows your skin to reflect more light and look more radiant.
- Fading pigmentation: Since they both encourage the shedding of old, discoloured dead skin cells, AHAs and BHAs work to fade dark spots and even out skin tone.
- Firming and reducing wrinkles: At higher concentrations, AHAs and BHAs have been shown to increase the density of collagen in the dermis. That means they can both help to reduce fine lines and wrinkles and improve skin firmness over time.
- Hydrating: AHAs and BHAs are both humectants—ingredients that help your skin to attract and hold more moisture.
- Clearing and preventing acne: AHAs and BHAs both help with acne by exfoliating the surface dead skin that can lead to clogged pores.
How AHA and BHA Are Different
There are, however, some important differences between AHAs and BHAs:
- BHAs penetrate more deeply: Since AHAs are water-soluble, they only exfoliate the skin’s surface. BHAs are oil-soluble, so they can pass through sebum and get deep into the pores.
- BHAs reduce oil production: While AHAs don’t have an effect on sebum, BHAs actually slow down its secretion to help control oily skin.
- BHAs are more effective for acne: Although both acids can help with mild acne by sloughing off dead skin cells, BHAs also work their magic underneath the skin surface. By deep-cleaning the pores, BHAs not only clear existing breakouts but also help to prevent them long-term. I consider BHAs to be the most effective topical treatment for acne.
- BHAs “shrink” pores: Technically, you can’t change the size of your pores—but they can look bigger when they are filled with debris. While AHAs don’t affect pores, BHAs can help them to look smaller by keeping them clean.
- BHAs are less irritating: Any acid can be drying and irritating if you use it at the wrong concentration or pH, or if you apply it too frequently for your skin. However, AHAs (especially glycolic acid) are more often associated with irritation, redness and inflammation. BHAs are gentler due to their larger molecule sizes, anti-inflammatory benefits and lower required concentrations. According to the late Dr. Albert Kligman (who conducted many studies on hydroxy acids), AHAs need to be used in concentrations of at least 8% in order to be effective, whereas BHAs only need a concentration of 1.5-2%.
- AHAs cause photosensitivity: It’s well-known that AHAs increase your skin’s sensitivity to the sun, making it more vulnerable to sun damage and premature aging. While sunscreen is essential always, BHAs actually have some photoprotective effects.
- AHAs cause skin wounding: As I mentioned above, AHAs are skin-wounding agents because they encourage cells to self-destruct through apoptosis (programmed cell death). BHAs are non-wounding agents, as they simply dissolve the “glue” between skin cells—which is a more physiological process. Is apoptosis or cell death something to worry about? Maybe, if you’re using strong AHAs on a regular basis. Apoptosis is also induced by toxins such as estrogen, unsaturated fatty acids and radiation, and has been described as “a cellular endpoint of the stress response.”
Should You Use AHA, BHA or Both?
Now that you’re familiar with the similarities and differences between AHAs and BHAs, what does that mean for your skincare routine? Here are my thoughts:
If You Have Acne
BHAs are the way to go. Salicylic acid is proven to reduce the number and severity of acne lesions, and is superior to benzoyl peroxide. Look for a concentration of 2% salicylic acid or its equivalent, 4% betaine salicylate. Keep in mind that you may experience initial purging, which is normal and beneficial. See my skin purging vs breakout tutorial for more information.
If You Have Oily Skin
Only BHAs will reduce your oil production. It may take some experimentation to find the best dose for your skin. I suggest between 1-2% salicylic acid, or 2-4% betaine salicylate.
If You Have Dry or Sensitive Skin
Lactic acid is the best AHA for these concerns, as it’s one of the gentlest and most hydrating acids. Look for a concentration between 5-8% percent to start, moving up as high as 10% if tolerated. However, a mild BHA would be an equally appropriate option, such as 0.5-1% salicylic acid or 1-2% betaine salicylate.
If You Have Pigmentation
Both AHAs and BHAs will help, but I think BHAs are your best bet—especially if you have darker skin. Unlike AHAs, they won’t trigger post-inflammatory hyperpigmentation, which is a risk for many ethnicities. Since BHAs also give you some photoprotection, you’ll be at less risk of creating new pigment, too. Go for a higher concentration if you can, such as 2% salicylic acid or 4% betaine salicylate. To target discolourations even further, use it in conjunction with niacinamide (see this tutorial for layering tips!).
If You Have Wrinkles
Both AHAs and BHAs have been shown to have a thickening effect on the dermis, the middle layer of skin with collagen and elastin fibers. For best results, you’ll want around 8% (or more) glycolic or lactic acid, or 1-2% percent salicylic acid. Again, just keep in mind that AHAs (particularly glycolic acid) can make your skin more inflamed and vulnerable to sun damage, which can exacerbate signs of aging.