Acids Decoded: What Are AHAs, BHAs And PHAs In Skincare?

Acid — the very word is enough to trigger uncomfortable thoughts of sore, tingling skin for those who aren’t in the beauty know.

And for those who are? Well, they know that incorporating acids into a regular skincare regime is the answer to a pretty much flawless complexion.

From Alpha Hydroxy Acids (AHAs) and Beta Hydroxy Acids (BHAs) to the new acids on the block for 2018, Polyhydroxy Acids (PHAs), these hard-working chemical exfoliants can minimise acne, erase pigmentation and blur fine lines — and that’s just the tip of the iceberg.

The best part? You don’t need a degree in chemistry to know how to use them, and thanks to brands like Glossier and The Ordinary, you won’t be left with red raw cheeks, either.

What Are AHAs In Skincare?

“AHAs are chemical exfoliators that can be extremely helpful for oily or blemish-prone skin if used on a regular basis,” says Dr. Anjali Mahto, consultant dermatologist and British Skin Foundation spokesperson.

The most common AHAs in skincare are glycolic acid and lactic acid. These work by dissolving the upper layer of dead skin cells to blur red marks left behind by acne, erase pesky patches of pigmentation, and, if you suffer with minor breakouts or bumpy, uneven skin texture, prevent spots from popping up with consistent use.

What’s the difference between lactic acid and glycolic acid?

Well, glycolic acid has a smaller molecular size than lactic acid, meaning it can penetrate the skin a little better.

Because of its slightly larger molecular size, lactic acid is a bit less irritating on the skin, but works in the same way — by sloughing off the top layer of skin cells to reveal fresher, brighter, plumper skin underneath. Both improve the skin’s moisture levels, too.

Pro Tip: Acids come in varying strengths, so talk to a dermatologist if you’re finding it tricky to determine the right percentage for your skin type.


ordinary acid
The Ordinary Lactic Acid 10% HA 2%

Blast under-the-skin bumps and blocked pores with a nightly slathering of this stuff. Choose between either 5% or 10% lactic acid to turf sebum, grime and dead cells out of pores at record speed. The added hyaluronic acid prevents the skin from feeling tight and dehydrated.

What Are BHAs In Skincare?

BHAs are also chemical exfoliators but they’re better catered to oilier skin types that are prone to acne, blackheads and milia, AKA those annoying little white bumps under your skin.

Why? Not only do they exfoliate the top layer of skin, but they can penetrate blocked pores by making their way into the oil glands, dissolving the paste-like mixture of sebum and dead skin that can lead to spots. The most popular BHA in skincare is salicylic acid.

“Exfoliating with a leave-on BHA that contains salicylic acid is a game-changer,” says Paula Begoun, skincare specialist and founder of Paula’s Choice. “It gets rid of dull cells but doesn’t strip the skin’s essential oils.”

Salicylic acid is also a proven anti-inflammatory, which means it’s perfect for calming raging zits and reducing pigmentation or redness caused by acne.

Even better? Using AHAs and BHAs together delivers a double-pronged attack on stubborn skin concerns like acne, sun damage and clogged pores, exfoliating the skin more thoroughly. Simply alternate between an AHA product and a BHA product either each evening or weekly, or grab one that contains both.


paulas choice acid skincare
Paula’s Choice Skin Perfecting 2% BHA Liquid Exfoliant

Blackheads don’t stand a chance against this leave-on exfoliant. Make sure your skin is squeaky clean, decant a few drops onto a cotton pad and swipe. It doesn’t tingle or feel sticky on skin.

What Are PHAs In Skincare?

There’s a new complexion-perfecting acid on the block for 2018 and it’s a must-have for those with sensitive skin.

“PHAs (AKA polyhydroxy acids) are very similar to traditional alpha hydroxy acids, because both work by breaking down the ‘glue’ that binds dull, dead cells to the surface of the skin,” explains Daniel Issacs, Head of Formulation and Development at Medik8.

So what sets PHAs apart?

“Their difference lies within their molecular structure,” explains Daniel. “The molecules that make up PHAs are much larger in size, which means they cannot penetrate skin as deeply as traditional AHAs and BHAs. Instead, they work exclusively on the skin’s surface without disturbing the delicate layers that lie beneath. This ensures optimum skin renewal with minimal irritation.”

They’re especially beneficial for those who find other acids too strong. “Even very sensitive skin types can harness the resurfacing powers of PHAs,” says Daniel. “In clinical studies, they have been proven to be compatible with dry, itchy skin conditions such as eczema and atopic rosacea.”


glossier solution acid
Glossier Solution

With a mega-mix of AHAs, BHAs and PHAs, the newest addition to Glossier’s skincare line promises clearer, more radiant skin — and boy, does it deliver. We’ll take two more bottles, please.

Remember To Always Apply An SPF When Using Acids

Whatever percentage, acids have a tendency to make skin sensitive to things like UVA, so slathering on the SPF during the day is paramount to keeping your glow.

“SPF is important if treatments are being applied to the skin that are causing exfoliation, e.g. AHAs, BHAs,” says Dr. Anjali. “The skin is more vulnerable to damage and pigmentation change following these types of treatments and pigmentation can potentially get worse if SPF is not applied.”