The A to P of exfoliating acids: AHAs, BHAs and PHAs explained

Exfoliation is necessary for normal, healthy, functioning skin. It’s so important that our skin does it naturally and constantly! Desquamation is your skin’s natural exfoliating process, where fresh, baby skin cells travel up to the surface and old dead one’s are sloughed off. This process is also referred to as cell turnover. Cell turnover slows down as we age, as well as by dehydration and exposure to environmental stressors, so we help the process along by exfoliating. (For a look at what it means to exfoliate and the different ways, check out Exfoliation 101).

Chemical Exfoliation

By breaking down the bonds between dead skin cells on the surface, chemical exfoliants can help to increase cell turnover, providing both immediate and long term benefits. Immediate benefits can include smoothness and radiance, while long term may help to stimulate collagen production, unclog pores, reduce hyperpigmentation and even skin tone.

There are 3 main categories of exfoliating acids: alpha hydroxy acids (AHAs), beta hydroxy acids (BHAs) and polyhydroxy acids (PHAs). The primary difference between these exfoliants is their molecular size, though they also have some unique properties.

A 4th related type of chemical exfoliation is enzyme exfoliation. Enzymes are often also formulated with other exfoliating acids.

How to Choose

Chemical exfoliants can be found in pretty much every skincare product including cleansers, toners, serums, masks and even moisturizers. Some products are safe to be used daily, while others should be reserved for occasional use. You can often find products with more than one type of acid, including our own Balancing Act Serum.

Finding the right type and frequency of acid can take some trial and error, but as with all things, start slowly and stick to 1 or 2 products. To help you start to narrow down, we’ve included key information about each type of acid below. But first, some general tips for everyone:

The smaller the molecule, the more potential for irritation because it can penetrate deeper into the skin.
When starting a new exfoliating product, use it a few times a week for at least 2-3 weeks before upping your frequency of use. Slow and steady wins the race!
Be mindful of ways you may already be exfoliating your skin to avoid over exfoliation, such as washcloths, cleansing devices or even rubbing too hard while cleansing! Avoid these physical methods of exfoliation all together if you have inflamed acne. (If you think you may have over-exfoliated, here are some tips to help you bounce back.)
It’s a common misconception that acids need to sting or burn in order to be effective. Mild, temporary stinging is a normal sensation, but should be tolerable and subside quickly, within a few minutes. Any extreme stinging, burning or raw feeling are indications that you need to take a step back and wash it off.

AHAs

Alpha Hydroxy Acids, or AHAs, are the most common exfoliating acids. They are typically derived from fruits, nuts or dairy and include glycolic, lactic, mandelic, malic, tartaric and citric acid. AHAs are generally water-soluble and have varying molecular sizes. In addition to exfoliating the surface layer of skin, they can also stimulate collagen production, increase hydration and help with congestion. The most common players are glycolic, lactic and mandelic acid, so we’ll focus on them.

Glycolic acid is derived from sugarcane. It’s the smallest AHA and can penetrate the deepest. Because of its ability to stimulate collagen production, it can help tighten and firm the skin and is a particularly good choice for anyone whose primary concern is signs of aging. It may cause stinging or be too irritating for anyone with sensitive or dry skin. Look for concentrations of 5-10%.

Lactic acid is derived from milk or tomatoes. It’s much larger than glycolic acid and therefore tends to be much gentler. In addition to gently exfoliating the surface, lactic acid has humectant properties and may help to increase hydration and barrier function. Anyone can use lactic acid, but it’s an especially good choice for dry, sensitive, dull or dehydrated skin. Look for concentrations of 5-10%.

Mandelic acid comes from bitter almonds and is the largest and gentlest AHA. It also happens to be our favorite acid! Unlike other AHAs, mandelic acid is oil-soluble, allowing it to penetrate deeper into pores, while still being non-irritating. In addition to exfoliating the surface, fading dark spots and stimulating collagen, mandelic acid uniquely has antibacterial properties. For all of these reasons and more, mandelic acid is a great choice for acne-prone skin, from the most sensitive to the oiliest. Look for 5-11% concentrations, like our Balancing Act Serum, which has 8% mandelic acid.

BHAs

There’s really only one type of BHA: salicylic acid, which comes from willow bark. Salicylic acid is oil-soluble, so it is able to exfoliate down into the pore to unclog and clear congestion. It is also anti-inflammatory, making it a great choice for clearing and preventing congestion. If you don’t struggle with acne or clogged pores, you probably don’t need to use a BHA. Look for concentrations of 0.5-2%. Our Balancing Act Serum has 0.5% salicylic acid.

PHAs

Polyhydroxy acids, or PHAs, are newer in the skincare world but becoming increasingly popular due to their gentleness and versatility. PHAs have the largest size of any exfoliating acid, allowing them to very slowly penetrate the skin and gently exfoliate the surface. In addition to offering super gentle exfoliation, PHAs are also water-attracting humectants. Anyone can use PHAs, but they are especially good for sensitive, dry or dehydrated skin. Look for concentrations around 10%.

The most common PHAs are gluconolactone and lactobionic acid. Both are powerful antioxidants, able to neutralize free radicals (which exacerbate signs of aging and dehydration) as well as improve barrier function. Our Soothe Operator Silky Gel Cleanser has gluconolactone and is safe for all skin types, twice a day.

Enzymes

Enzymes break down protein bonds on the surface of the skin and digest dead skin cells. Since they’re primarily working on the surface of the skin and not penetrating deeper, they’re particularly gentle. They can gently resurface and brighten the skin, plus most are anti-inflammatory! They may tingle a bit as they get to work, but are generally safe for all skin types. The most common enzymes in skincare are bromelain/Ananas sativus fruit extract (derived from pineapple), papain/Carica papaya fruit extract (derived from papaya) and Cucurbita pepo (did you guess this one? It’s from pumpkin!).