Wondering whether you should try an AHA, a BHA - or both?
These two types of acid exfoliants are popping up in more products than ever before, and often together! So you might be confused about which one(s) would be best for your skin, what results you can expect, and if it's a good idea to combine them.
What is an AHA?
HA stands for alpha-hydroxy acid—a type of acid that is derived from sugarcane, milk or fruit. As chemical exfoliators, AHAs work by peeling away the dead skin cells on the skin surface, revealing the fresh new skin cells underneath.
But how exactly do they do that? According to a study, AHAs exfoliate by reducing the concentration of calcium ions within the epidermis and the "glue" between skin cells, which allows them to be sloughed off. But more recent studies have found they do so by causing a type of cell death known as apoptosis. More on this in a second!
Here are the different types of AHAs you'll 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.
- 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: An AHA derived from grapes. Instead of acting as an exfoliant, it is more often used to stabilize other acids' pH levels.
- Citric acid: An AHA derived from citrus fruits. It is similar to tartaric acid in that it regulates pH. It is also used as a preservative.
What is a BHA?
BHA stands for beta-hydroxy acid, a type of acid found in willow tree bark, wintergreen leaves or sweet birch bark. BHAs are chemical exfoliators that soften and dissolve keratin, a protein that forms part of the skin structure. This helps to loosen dead skin cells, so they're easily sloughed off. BHAs also work inside the pores, where they not only dissolve keratin plugs, but also help to regulate keratinization (cell turnover and shedding).
For example, a condition like acne is associated with hyperkeratinization—meaning the body is shedding skin cells too fast. BHAs slow down this process, so the cells function longer before they flake off (meaning they're less likely to clog pores).
The main BHA exfoliants you'll see in skincare products are:
- Salicylic acid: The most common BHA, and also the strongest BHA. However, it is not as irritating as glycolic acid (the strongest AHA) because it has a large molecule size, as well as anti-inflammatory properties.
- Betaine salicylate: A BHA derived from sugar beets. It is a gentler alternative to salicylic acid, and according to a study by the manufacturer, is equally effective. (Four percent betaine salicylate is said to be equivalent to two percent salicylic acid.)
- Salix alba or willow bark extract: A natural BHA extracted from plants. Although the salicin content converts into salicylic acid, it is much weaker (so it won't give you comparable results for exfoliating or treating acne).
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.
Not true! These are all the benefits that BOTH AHAs and BHAs have in common:
- Exfoliating and smoothing: Although they have different mechanisms, AHAs and BHAs are both effective at removing dead skin cell build-up and smoothing the skin.
- Brightening: Both AHAs and BHAs reduce the thickness of the stratum corneum (the top layer of skin consisting of dead skin cells). That means skin will reflect more light and look brighter.
- Fading pigmentation: Since they both encourage the shedding of old, discoloured dead skin cells, AHAs and BHAs can help fade dark marks and even out skin tone.
- Firming and reducing wrinkles: Both AHAs and BHAs have been shown to increase the density of collagen in the dermis, which means they could help reduce fine lines and wrinkles and improve skin firmness over time.
- Hydrating: AHAs and BHAs are both humectants—ingredients that attract water and help your skin retain moisture.
- Clearing and preventing mild acne: AHAs and BHAs both help with acne by exfoliating the dead skin that can lead to clogged pores.
How AHA and BHA are different?
There are, however, some important differences between AHAs and BHAs:
- Solubility: AHAs are water-soluble, so they dissolve in water. BHAs are oil-soluble, so they dissolve in oils (meaning they can pass through sebum and sebaceous follicles).
- Area of action: AHAs work on the top layers of skin, but BHAs work on the skin surface AND inside the pores.
- Concentration: According to Dr. Albert Kligman, AHAs need to be used in concentrations of at least eight percent in order to be effective, whereas BHAs only need a concentration of around two percent. (And nowadays, BHAs can be found in doses as low as 0.5 percent.)
- Decreasing oil production: AHAs don't have an effect on sebum. BHAs can reduce excess oil by slowing down sebum production.
- Clearing and preventing acne, blackheads and clogged pores: While both acids can help with mild acne (by sloughing off dead skin cells), BHAs also work on a deeper level to clear trapped sebum in the pores and prevent new clogs from forming. They also slow down oil secretion and loosen blackheads, making them easier to extract.
- "Shrinking" pores: Technically, you can't change the size of your pores—but they can look bigger when they are filled with debris, which makes them stretch out. While AHAs don't affect pores, BHAs can help them look smaller by keeping them clean.
- Irritation: 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 are more often associated with irritation, redness and inflammation. BHAs tend to be less irritating, thanks to their larger molecule sizes. They also have anti-inflammatory properties.
- Photosensitivity: 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.
- Skin wounding: 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 loosen the bonds between skin cells (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 this paper describes it as "a cellular endpoint of the stress response."
AHA, BHA or both?
Now that you know the differences between AHAs and BHAs, what does that mean for your skin concerns?
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 two percent salicylic acid or its equivalent, four percent betaine salicylate. Keep in mind that you may experience initial purging (which is a good thing!).
If You Have Oily Skin:
Only BHAs will reduce oil production. It may take some experimenting to find the best dose for your skin—between 0.5 to two percent salicylic acid, or one to four percent 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 five to eight percent to start, moving up as high as 10 percent if tolerated. However, a mild BHA would be an equally suitable option, such as 0.5 to one percent salicylic acid or one to two percent 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. BHAs also have some photoprotective properties, so you're less likely to create new pigment. Go for a higher concentration if you can, such as two percent salicylic acid or four percent betaine salicylate. For best results, use it in conjunction with niacinamide (see this tutorial for layering tips!).
If You Have Wrinkles:
Glycolic acid, lactic acid and salicylic acid have all been shown to produce changes in dermal thickness and the depth and number of fine lines and wrinkles. For best results, you'll want around eight percent (or more) glycolic or lactic acid, or one to two percent salicylic acid. Again, just keep in mind that AHAs can make your skin more inflamed and vulnerable to sun damage, which can exacerbate signs of aging.
If You Want to Combine Acids:
And what about AHAs and BHAs together? Is there any benefit to using both?
Not really! Salicylic acid does everything AHAs do and more, and does it more effectively. So if you have a good BHA, you don't need an AHA as well.
Still want to incorporate both in your routine? Try one of these options:
- Use a combo AHA-BHA treatment with a mild blend of acids. (Product suggestions below!)
- Apply your AHA and BHA at different times of day. I suggest using your BHA in the morning (since it's not photosensitizing) and your AHA at night. Or, you could apply them on alternate nights.
- Apply your BHA on your oilier areas (like in your T-zone), and your AHA everywhere else. That way, you're applying both at the same time, but not doubling up on acid.
- Layer one acid on top of the other—but this does increase your risk of irritation and dryness! Since AHAs and BHAs are close in pH (between 3.0 and 4.0), you wouldn't need to wait in between; just apply the product with the thinnest texture and/or lowest pH first.
Now you know the differences between AHAs and BHAs!
But no matter which acid you choose, the key is finding one that's the right strength for your skin, and not overdoing it. I believe you'll get better results from using a milder acid on a regular basis—as often as daily—instead of shocking your skin once a week with a strong, irritating peel.