The Difference Between AHAs and BHAs In Skin Care

Sable Yong
Getty Images / Maria Toutoudaki

Getty Images / Maria Toutoudaki

Anyone chasing smooth, even, and clear dewy skin has probably heard of AHAs and BHAs. Perhaps you’ve seen it as a footnote on the bottle of your cleanser, serum, or exfoliator. You know it’s a good thing, but you’re not really sure what it is or how it works. If you’ve been using a manual exfoliator with scrubby bits in it, we’re just about ready to slap it out of your hands from all the damage you’re likely doing to your skin. If all you needed to know was a little bit about how these chemical exfoliators worked to dive in to them, by all means, read on.

AKA “Alpha Hydroxy Acids”, AHAs are what you can consider the Goo-Gone of dead skin debris. The weak bonds that keep that layer of dead skin on your hide are essentially dissolved with AHAs so your skin can let go of the dead stuff and let the new skin cells surface. AHAs are great chemical exfoliants for people with dry and sensitive skin, since they can help remove dead skin in the gentlest way possible that doesn’t involve manually buffing them off (which harms the new skin underneath too).

AHAs also have humectant properties, meaning they hold moisture to your skin. Aside from daily skin-clearing, over time AHA use helps to thicken the epidermis and increase collagen production—all of which is excellent for repairing photo-damaged skin as well as protecting it from future UV damage. Extra collagen means firmer plumper skin. So as far as anti-aging concerns go, you’ve got two birds with one stone. The caveat is that AHAs do cause photosensitivity so they should be used at night only and you should always wear a broad spectrum sunscreen during the day (but you were already doing that, right?).

The most common AHAs are Glycolic Acid, Lactic Acid, and Mandelic Acid. Keep in mind that these are strong substances and should be used in very small percentages. Not sure which ones to use? Here’s a tiny tip sheet:

  • Glycolic: Probably the most common AHA because it has the smallest molecular size, meaning it can penetrate your skin the deepest for repair (but also can be potentially the most irritating if you go overboard). Go for lower percentages (less than 10%) when trying them out and work your way up as needed.

MORE: Why Glycolic Acid Is Your Skin Care Must 

  • Lactic: This is a milk-derived acid which happens to be great for addressing redness issues like roseacea and sensitive skin in general. It is also a humectant so it won’t over-dry your skin as it helps slough off that top layer.
  • Mandelic: This one is great for acne-prone skin because of its anti-bacterial and anti-viral properties. It has the largest molecular size of these AHAs which just means that it works over a longer time period, but is also the least irritating. This one is also a milk humectant.

They may be Beta Hydroxy Acids, but make no mistake–these acids are no wimps. They are however your secondary selection if AHAs just aren’t tough enough for your skin. BHAs are generally encouraged for oily and acne-prone skin since they are oil soluble (while AHAs are water soluble), making them perfect for treating blackheads, whiteheads, and acne. Rather than just loosen the bonds that hold debris to your skin, they actively penetrate your pores and remove whatever gunk is in there.

Cosmetically, BHAs almost always refer to salicylic acid—something you’ve no doubt seen on almost any acne treatment.  Salicylic acid is a derivative of aspirin—a known anti-inflammatory—which makes it great for relieving your skin of any inflammation (but also not great if you have aspirin allergies—sorry). It’s also commonly found in dandruff treatments since it’s can calm irritation on your scalp as well as sloughing away the dead skin that’s flaking.

One of the better benefits of BHAs are that in clearing your pores of any gunk, whatever treatments you then put on top of your newly cleaned skin can absorb properly. So, anti-aging serums? Brightening agents? All good to go 100% once your canvas is cleared. BHAs themselves give you similar skin benefits to AHAs, like helping increase the thickness of skin, as well as collagen production, and improves wrinkles, roughness and hyperpigmentation. They don’t possess humectant qualities however and can dry out your skin, so this is why it’s not generally recommended for those with dry skin.

How to use them?
Unless you’re a skin care layering pro, it can be confusing as to where these magic skin potions go in your skin care sandwich. They should be applied on clean skin so there’s no extra stuff to have to fight through to get down to business— so after cleansing and toning but before serums and moisturizers. And please don’t forget sunscreen as your last step!

MORE: The Guide To Exfoliation For Sensitive Skin