Asking for a Friend: WTF Are AHAs and How Do I Apply Them?


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It’s almost 2023, and by now, you’ve undoubtedly tried (or been pressured to try) a chemical exfoliant, whether it be a AHA vs. BHA vs. PHA. The only issue? Decoding WTF they all mean and figuring out which one to use—which is where I come in. As a quick refresher, AHAs (aka alpha hydroxy acids, like lactic and glycolic acid) are best for brightening dark spots and smoothing dry skin, while BHAs (beta hydroxy acids, like salicylic acid) are great for oily skin types and clogged pores. PHAs (poly hydroxy acids, like gluconolactone) help soften sensitive skin types, but are also the least “potent” of the three.

But since you find yourself here (hello and welcome, plz stay a while), I’m going to assume you're desperate for a no-bullshit breakdown of alpha hydroxy acid for skin (~AHAs~). And fear not—I’ve got you. I chatted with two board-certified dermatologists, Karan Lal, MD, and Kristina Collins, MD, to find out everything you need to know about AHAs, starting with what they are, what skin type they’re best for, how to use them, and more.

What are AHAs?

Alpha hydroxy acids—aka AHAs, including lactic, glycolic, malic, tartaric, and mandelic acids—are water-soluble acids that sink into the surface of your skin and dissolve the glue that binds old skin cells together, so they slough off and leave your skin looking brighter and smoother. Most AHAs also have a bit of humectant properties to them (i.e., they’re able to pull water from the air into your skin), so they’re slightly more hydrating than other chemical exfoliants, like BHAs (or salicylic acid).

What are the different types of AHAs?

There are surprisingly a ton of different types of alpha hydroxy acids available, all of which have varying strengths and molecule sizes, meaning virtually anyone (even sensitive-skin types) can find an AHA that works for them. The most common AHAs are:

Glycolic acid

Glycolic acid is actually derived from sugarcane, and Dr. Lal deems it “the gold standard” of alpha hydroxy acids in terms of efficacy. Why? Because glycolic acid has the smallest molecule size of all the AHAs, which means it can penetrate the skin the deepest and most efficiently. But, on the flip side, its molecule size is also what makes it the most potent of the AHAs.

Lactic acid

Perhaps the least-yummy thing you'll hear today is that lactic acid comes from spoiled milk (sorry). Don't let that deter you, tho! She's still cute! Dr. Collins dubs lactic acid the "gentler cousin to glycolic acid" because it has a larger molecular weight and can't penetrate the skin as profoundly, making it easier for sensitive skin to tolerate.

Mandelic acid

Mandelic acid—derived from bitter almonds—tends to be gentler than lactic and glycolic acid, and also has antimicrobial and antibacterial properties that make it a great choice for acne-prone skin. It’s even been shown in clinical studies to help reduce oil production on oily skin types (whereas glycolic acid did not).

Malic acid and tartaric acid

These brightening AHAs come from fruit (lemons, apples, and grapes) and are the "least potent and the most gentle of the AHAs," says Dr. Lal. They’re a great option for first-time alpha hydroxy users with highly sensitive skin, but don’t expect miracles—they’re too weak to treat acne or major hyperpigmentation.

Benefits of alpha hydroxy acid for skin

  • Exfoliates skin: AHAs help break down dead skin cells over time, leaving you with newer, fresher, brighter skin within a few weeks of continual use.

  • Softens fine lines: According to Dr. Collins, alpha hydroxy acids—specifically glycolic acid—can help facilitate the production of collagen, which, over time, can result in smoother fine lines and wrinkles.

  • Treats acne: Though AHAs can’t penetrate as deeply into the skin as BHAs (salicylic acid, i.e., the top choice for breakouts and blackheads), they can help remove pore-clogging dead skin cells and fade acne scars.

  • Reduces hyperpigmentation: Alpha hydroxy acids, regardless of which one you use, will promote cellular exfoliation and help fade the brown, purple, or red marks that acne leaves behind.

How to choose the best alpha hydroxy acid

Think about your skin type

The first step to finding the best AHA is to identify whether your skin is dry, sensitive, oily, or combination. "If you're someone who has very dry or sensitive skin, start with gentle acids, like mandelic, tartaric, or lactic acid in low strengths,” says Lal. And “if you have combination, oily, or acne-prone skin,” he adds, “you'll likely benefit from glycolic acid.”

Pick the right concentration

Alpha hydroxy acids come in various forms (like cleansers, creams, serums, and toners) and concentrations (like 1 percent to 20 percent and higher). And because AHAs vary so wildly in potencies (i.e., 10 percent malic acid is significantly gentler than 5 percent glycolic acid), it’s impossible to create a clear-cut rule on choosing the right concentration.

So instead, Dr. Lal recommends starting with the lowest possible concentration of whichever AHA you do choose (i.e., start with 5 percent lactic acid or glycolic acid) and very slowly working your way up to stronger percentages with each bottle you finish.

Choose the formula strategically

If you're just starting out or have highly sensitive skin, Dr. Lal recommends trying an alpha hydroxy acid cleanser once a day, because it's only going to touch your skin for a short period of time. No redness, itching, or burning after three weeks? Great—try a serum, toner, or cream every few nights.

If, after you finish your bottle and think your skin can handle a stronger dose of AHAs, Dr. Lal says you can then venture into the world of high-strength AHAs, like peel pads or professional chemical peels. Because they’re the most potent, they’ll show the biggest results, but they’ll also destroy any face that hasn’t built up the proper tolerance first.

How do you use AHAs for skin?

To use alpha hydroxy acids on your skin, you’ll need to start low and slow: Pick a low-strength cleanser, toner, moisturizer, etc., and then use it once or twice per week, no matter your skin type, says Dr. Lal. After two weeks, you can start using it every three days for a few weeks, and slowly work your way up to every other day.

And don’t worry about feeling like you’re missing out on results by moving so slowly: “AHAs are an ingredient type that can give you serious benefits even without daily use,” says Dr. Collins. So be patient and trust the process.

What should you not mix with AHAs?

Good news: You don’t need to abandon your vitamin C or retinol if you want to start using an alpha hydroxy acid, but you do need to adjust your routine. A good rule of thumb, especially for those just starting, is to wait "12 hours between your AHA and your other actives,” says Dr. Lal. So, essentially, using your AHA in the morning and your retinol at night, or your vitamin C in the morning and your AHA at night.

The one thing you do want to avoid when using AHAs? Sun exposure, say both dermatologists. When using any active ingredient (including acids and retinoids), Dr. Collins recommends slathering on a mineral sunscreen of at least 30 SPF every morning (but you do that already, right? Right?!).

Though chemical sunscreens are still highly effective, Dr. Collins prefers mineral formulas, because “mineral sunscreen can truly coat the skin, blocking the penetration of UV rays.” With chemical sunscreen, however, “UV light can still trigger melasma or hyperpigmentation.” But, at the end of the day, the best sunscreen is the one you’ll actually wear, so please just protect yourself.

Is retinol better than AHA?

Neither retinol nor AHA is “better,” because they’re fundamentally different ingredients that work in different ways. Alpha hydroxy acids work on the surface of your skin to superficially exfoliate dead skin cells, while retinol (and retinoids in general) work beneath your skin to speed up cellular turnover and trigger collagen production.

That being said, both are “dermatology’s best weapons in terms of fighting skin aging,” says Collins. “Both increase collagen synthesis and increase the rate of cell turnover, which will leave you with glowier skin, fewer fine lines, and smoother texture.” Essentially, AHAs are a nap, while retinoids are an eight-hour sleep schedule—and your face will do better when you incorporate both of them at once.

What are the side effects of AHAs?

Let's start with the good (!) side effects that are often mistaken as bad: Tingling is frequently misinterpreted as a bad reaction, when it could mean that your AHA is doing its job (especially if its glycolic acid, which penetrates deeper into your skin). Typically, though, these “tingles” will decrease after a few weeks of adjusting to the formula.

If they don’t, you may be dealing with an adverse reaction—especially if your skin has been feeling itchy, tight, red, burning, or stinging. And, says Dr. Collins, if you experience a burning sensation that does not resolve in a few seconds, I would recommend washing off the product immediately.”

Other common side effects include redness, dryness, peeling, and being left with a chemical burn, but usually these side effects come from going overboard with a high-strength formula and "completely saturating your face" or "not following directions," says Dr. Lal. But fear not: If you've made it this far, you'll be A-okay. (I take tips.)

Which to choose: AHAS vs. BHA vs. PHAs?

Unlike water-soluble AHAs, BHAs are oil-soluble, so they penetrate deeper into the skin, says Collins. "Because of that, they're really great at controlling oil on the skin, unclogging pores, and treating acne," like blackheads and whiteheads. The downside is that BHAs, like salicylic acid, tend to be drying, so they can irritate already-dry skin types.

PHAs, on the other hand, have the largest molecular size of chemical exfoliants, which means they can't penetrate your skin as deeply as AHAs or BHAs. They’re “the best choice for ultra-sensitive skin,” says Collins, “but they do have less-pronounced clinical results.”

The bottom line

If you're looking to brighten your skin, even out your skin tone, and/or plump your fine lines, you should definitely add an AHA into your routine asap. Just make sure you spend your $$$ on a formula that actually works for your skin type, so remember to start low and slow, strategically pick the right formulation, and also memorize everything you just read. Sound good? Good.

Meet the experts:

  • Karan Lal, MD, is a board-certified dermatologist and the director of cosmetic dermatology at Affiliated Dermatology in Scottsdale, AZ. Dr. Lal specializes in pediatric and adult dermatology, laser surgery, and treating skin of color.

  • Kristina Collins, MD, is a board-certified dermatologist, CEO, and founder of Austin Skin dermatology in Texas. Dr. Collins specializes in Mohs micrographic surgery and surgical and cosmetic dermatology.

Why trust Cosmopolitan?

Marisa Petrarca is a contributing beauty writer for Cosmopolitan.com with over five years of experience researching and writing about makeup, skin, and hair, ranging from how to clean your makeup brushes to face fillers. She discussed all things AHAs with the dermatologists featured in this story and dove into reviews, research, and her collection of AHA treatments to recommend the best products.

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