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If you’ve ever taken a chemistry class, you’re probably familiar with the pH scale. (Hang tight, we promise we’re getting to acids for skin care.) While a seven is perfectly neutral, any substance that clocks in below that number below is considered acidic — and above it, basic. So by the scientific definition, tons of skin-care ingredients you don’t think of as acids — like, for example, vitamin C — could be categorized as such.
But it’s alpha and beta hydroxy acids (you may know them as AHAs and BHAs) that provide the exfoliating benefits typically associated with acids. In controlled formulas, these types of acids loosen the fluid that binds cells to the upper layers of skin, allowing the dead cells to fall away. This increase in cell turnover helps lessen breakouts, smooth fine lines, and gives an overall brightening effect. Pretty impressive, right?
But with great power comes great responsibility. So in this episode of The Science of Beauty, co-hosts Michelle Lee, editor in chief, and Jenny Bailly, executive beauty director, called in dermatologist Laurel Naversen Geraghty (who — fun fact! — is a former Allure editor) to help make sense of when and how to use these potent skin-care ingredients.
What are acids?
To put it simply, acids are a skin-care ingredient often used for exfoliation. Like we said, there are two main groups of acids in skincare: alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). Both groups loosen the fluid that binds cells to the upper layers of the skin — and once this happens, a smoother, brighter surface is revealed. As the acid dissolves the binding between skin cells, thousands of them usually come off at the same time. Depending on the strength of the acid, this shedding can actually be visible to the naked eye. Ever notice flakes falling from your skin after getting a peel? Yep, those are all dead cells.
What are the different types of acids used in skincare?
First, let’s unpack the difference between AHAs and BHAs.
AHAs are water-soluble and work mostly on the skin’s surface, making them a good option for treating fine lines, texture, and dullness. “Alpha hydroxy acids are probably the most common acids that are used for the skin,” explains Geraghty. “Those are really nice for exfoliating that outer layer of skin, leaving the skin brighter, evening out skin tone and texture, and they can even stimulate a little collagen production.”
BHAs, on the other hand, can penetrate deeply into clogged pores and are therefore helpful in treating and preventing acne. “Beta hydroxy acids actually bind to sebum — that's oil,” says Geraghty. So when those dead skin cells are swept away by a BHA, pore-clogging oil goes with them.
Within these two categories — AHAs and BHAs — are different acids with various skin benefits. Since choosing the best acid for your skin can be confusing, we broke down the most popular options for you.
The Best AHAs
Glycolic acid — which is derived from sugar — is one of the most common acids used in skincare. It has the smallest molecule of all the acids, so it penetrates the deepest, making it one of the most effective acids available. It regenerates collagen, thickens the skin, and evens out the skin tone. But there’s a catch to its dramatic results — since it penetrates so deeply and results in a more intense exfoliation, it also has a higher chance of producing irritation.
Lactic acid is the second smallest molecule out of all the acids. It’s gentler than glycolic and draws moisture to the skin, making it a hydrating agent, too. Created from sugar or fermented milk, this alpha hydroxy acid is gentle enough for people with sensitive skin.
Fun fact: Cleopatra was an early AHA adopter and took regular milk baths to improve her skin. “In ancient Egypt, women realized that the lactic acid found in milk had a softening, moisturizing effect on the skin,” explains Geraghty. Today, thousands of years later, “I find that a lot of people with rough, dry or flaky skin [still] rely on products [with lactic acid],” she adds.
Even gentler yet are fruit acids such as citric (which is typically derived from lemon or grapefruit) and malic (which usually comes from apples). These larger compounds work on the uppermost layer of the skin, and are often combined with glycolic or lactic acids to help boost their effectiveness.
The Best BHA
If you’ve ever bought an over-the-counter acne treatment, you’re probably familiar with salicylic acid — it’s one of the most popular ingredients for minimizing breakouts. That’s because salicylic acid penetrates and dissolves the oil that clogs pores while also exfoliating away dead skin cells. Even better, it works without irritating already inflamed skin, since it has anti-inflammatory properties.
But Wait… What’s Hyaluronic Acid?
It’s technically an acid because its pH is lower than neutral, but hyaluronic acid is really a humectant best known for its moisturizing properties. This sugar molecule is able to absorb up to 1,000 times its own weight in water and helps trap moisture against the skin’s surface. This kind of water retention allows plumping of the tissue and prevents moisture from escaping the skin, which can help soften the appearance of wrinkles.
How to Use Skin-Care Acids
What are the different ways to incorporate an acid into your skin-care routine?
Acids don’t just come in the form of peels. There are quite a few ways you can use them in your routine.
Some cleansers contain AHAs or BHAs and can provide some mild benefits — though many experts say it’s not enough to justify the high price tags on some of them. You might consider washing your face with a basic, gentle cleanser and then using an AHA cream or serum.
However, there’s one exception: If you have acne-prone or oily skin, a salicylic acid cleanser is worth buying since it’s a more targeted acid than the AHAs, seeking out oily, clogged pores and helping clearing them, even when only on your skin for a minute or two.
Other than cleansers, it’s common for acids to be infused in creams and serums, as well as treatments like masks or at-home peels.
How should you use an acid?
As a general rule of thumb, you should test the formula on your inner arm and wait 24 to 48 hours to see if you have a reaction. If you’re in the clear, you can try applying the acid on your face. While mild stinging isn’t a huge concern, any painful burning sensations are a big red flag. Once you find an acid-based cream, serum or mask that you like, you can use it one or two times a week and see how your skin reacts. After that, you can increase usage.
To use an at-home peel, follow these instructions: Wash face with a gentle cleanser and let your skin dry. Apply the solution over the T-zone and across the forehead, then fan out from the nose to cover the cheeks and chin. After that, rinse off the solution with water. Finally, apply a gentle moisturizer to soothe the skin.
And don’t forget the areas below your neck. Treat a blotchy chest by extending your AHA face cream a few inches south. Clear up back acne with a salicylic acid body wash or use an acid product on the backs of your hands since that area often shows signs of aging.
But no matter what area you’re treating or what kind of acid you’re using, please (please!) don’t forget to apply a generous coat of SPF, especially if you’re using anything acid-infused in the morning. Even if acids are only part of your nighttime routine, your skin is still extra-susceptible the next morning — so slather up.
At-Home vs. Professional Strength: Which is Best For You?
Both at-home acid products and in-office peels can give great results — as long as you choose the right one for you. The main difference between at-home peels and their in-office counterparts is their level of intensity. At-home peels usually have about 10 percent (or less) AHA or BHA, while professional formulas can contain up to 70 percent.
The higher concentration allows experts to reverse more-significant sun damage and fine lines. The longer the duration that the peel is left on the skin and the stronger the concentration, the deeper the peel penetrates. A series of three or four basic in-office peels can lighten dark spots and soften roughness without any downtime.
Superficial peels lift surface cells with a glycolic or salicylic acid solution. Experts recommend a minimum interval of two weeks between two treatment sessions. These are typically best for women in their 20s and 30s (with minor sun damage or acne) and are sometimes called “lunchtime peels” since there is very little downtime afterwards.
“[With] light peels, we may not see a lot of flaking, but we're still getting the benefit,” explains Geraghty. “We're still getting that radiant boost by microscopically helping to remove some of those outer layers of skin.”
These are best for women with dark spots, uneven tone, and fine lines from deeper sun damage. Medium depth peels are most commonly performed with glycolic acid, trichloroacetic acid (TCA), or Jessner’s solution, which is a mixture of lactic acid, salicylic acid, and an antiseptic exfoliant. These peels treat hyperpigmentation and fine lines that extend into deeper layers of the epidermis. This stronger acid can burn more intensely, and doctors may prescribe pain pills. Since this process is more intense, the downtime is longer, meaning the skin is red or brown for up to a week until a crust forms over the face. That leathery surface then flakes off to reveal brighter, smoother skin.
Buyer beware: If raw, sunburned-looking skin is what you associate with in-office peels, you’re not off from the aftermath of a deep in-office peel. These can make skin visibly slough away in an almost-scary way, but the eventual results are the most dramatic.
These types of peels are best for women with etched-in wrinkles around the eyes and mouth, deep acne scars, and stubborn dark spots. The phenol peel, a chemical treatment so intense that it often requires cardiac monitoring, was once the only option for addressing these skin concerns. Recovery time is brutal, and after a phenol peel, your skin crusts over and peels off over the course of about 10 days. “This is not for the faint of heart,” warns Geraghty. “Those hardcore, deep peels are very aggressive, but they can have beautiful results, too. So for tough patients, they can get through them.”
Our Hosts’ Favorite Skin-Care Acids
Michelle’s Current Favorites
Michelle is a major fan of Dr. Dennis Gross Skincare Alpha Beta Universal Daily Peel, a two-step treatment with both AHAs and BHAs that’s gentle enough for daily use. For an extra boost, Michelle loves to apply Peach & Lily Super Reboot Resurfacing Mask, which combines a blend of acids with soothing ingredients like aloe and chamomile.
Jenny’s Current Favorites
Jenny has professed her love for Biologique Recherche Lotion P50 on the podcast before — but since its glow-producing power comes from lactic and citric acids, she’d be remiss not to mention it again. And for a more intense weekly sloughing, Jenny likes Drunk Elephant T.L.C. Sukari Babyfacial. The mixture of glycolic, lactic, citric, and salicylic acids brightens skin in just one application.
And proving there’s nothing they won’t do in the name of science, both Michelle and Jenny tried Baby Foot in preparation for this episode. The exfoliating treatment involves inserting your feet into disposable booties filled with a blend of citric, lactic, and salicylic acids. Though neither noticed changes immediately, days later, both Michelle and Jenny reported their feet started shedding “like snakes.” (Their words, not ours!) Though their families had mixed feelings about finding trails of dead skin on their floors, Michelle and Jenny were impressed with how soft their heels looked and felt — and will continue to use BabyFoot anytime their feet need some TLC.
The Bottom Line
Congratulations — you’re now an unofficial graduate of Acids 101. The main takeaway? Face acids are your friends. When used correctly, they can have a lasting effect on the texture and tone of your skin.
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