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Skin cells typically regenerate every month or so. But things like sun exposure and aging can slow this process down.

That’s where exfoliation comes in handy. A quick way of removing dead skin, it can do everything from brightening your complexion to fading acne scars.

Two types of exfoliation exist: physical and chemical. The chemical type, consisting of a range of different acids, has become increasingly popular in recent years.

But there’s still some confusion over what it actually is and which acids are best to use. Here’s what you need to know.

The following acids can be used to treat these common skin concerns across each skin type.

Keep reading our guide to learn how to use them, get product recommendations, and more.

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Chemical exfoliants are acids that get rid of dead skin cells. They come in various concentrations.

Weaker formulas can be bought over the counter, while stronger ones are usually applied by a dermatologist in the form of a chemical peel.

They work by breaking the bonds that hold skin cells together, says board-certified plastic surgeon Dr. Michelle Lee.

“As those bonds are broken, the top layers of the skin cells shed, revealing regenerated skin,” she says.

With regular use, skin feels smoother and looks more even in tone, pores are unclogged, and signs of aging may be less apparent.

While acids chemically remove the outer layers of the skin, physical exfoliants do so manually.

Taking the form of scrubs, brushes, and procedures like dermabrasion, physical exfoliation can be too harsh for some.

It also doesn’t penetrate as deeply as the chemical version and therefore may not be as effective.

There are three main types of chemical exfoliant. All are acids, but some are gentler and less penetrative than others.

The main thing to remember is the higher the concentration and lower the pH, the more intense the exfoliative effect.

Alpha hydroxy acids (AHAs)

AHAs include the likes of glycolic, lactic, citric, and malic acid. They tend to come from fruits, but can also be produced synthetically.

With the ability to dissolve in water, they work on the surface of the skin to improve its texture, notes dermatologist Dr. Hadley King.

Glycolic and lactic acid are commonly used AHAs in skin care. Opt for a concentration of between 5 and 10 percent for high effectiveness.

Beta hydroxy acids (BHAs)

BHAs are oil-soluble, so they can penetrate your pores, as well as work on the skin’s surface, explains King.

These deeper-working acids not only benefit skin texture, but also unclog pores and remove acne-causing sebum.

Examples of BHAs include salicylic acid and tropic acid.

Poly hydroxy acids (PHAs)

PHAs work in a similar way to AHAs. “The difference is that PHA molecules are larger, so they cannot penetrate as deeply,” says King.

This is why they’re viewed as less irritating than other chemical exfoliants, particularly AHAs.

And although they don’t go as deep, PHAs — like gluconolactone and lactobionic acid — have additional hydrating and antioxidant benefits.

AHAs are often used to improve skin tone and mild areas of discoloration.

BHAs, on the other hand, are ideal for oily or acne-prone skin due to their pore-unclogging properties.

If you have highly sensitive skin, a less intrusive PHA exfoliant may be the route to go down.

Whichever acid you decide to use, start off slowly. Try applying once a week to see how your skin reacts, increasing to two or three times a week if no irritation occurs.

Still not noticing results after 2 months? Switch to a different chemical.

Certain skin types gain more from AHAs, BHAs, and so on. Figure out your skin concern and you’ll be on your way to finding the right hydroxy acid.

If you have dry or sensitive skin

BHAs can soothe and calm skin, making them ideal for sensitive skin types or people who experience redness.

But PHAs, found in Zelens’ Bio-Peel Resurfacing Facial Pads, are also an option for sensitive types. Studies have even found that PHAs are suitable for people with eczema and rosacea.

Shop for Zelens’ Bio-Peel Resurfacing Facial Pads online.

If you have dry skin, opt for an AHA. As they only work on the skin’s surface, they’ll help it cling onto moisture. The Ordinary’s Lactic Acid comes highly rated.

Shop for The Ordinary’s Lactic Acid online.

If you have oily or acne-prone skin

BHAs, particularly salicylic acid, are great for clearing pores of all the substances that can lead to breakouts.

Thinner liquid formats are ideal for oily skin — try Paula’s Choice Skin Perfecting 2% BHA Exfoliant.

Shop for Paula’s Choice Skin Perfecting 2% BHA Exfoliant online.

“A potential downside to using salicylic acid is that it can make the skin feel drier,” notes King.

She recommends combining it with lactic acid, an AHA, to “improve the skin’s natural moisture factor.”

If you have combination skin

Combination skin requires the best of both worlds. Go for a serum containing salicylic acid for an anti-inflammatory exfoliating effect.

Caudalie’s Vinopure Skin Perfecting Serum has a lightweight gel texture that won’t clog pores or dry skin out.

Shop for Caudalie’s Vinopure Skin Perfecting Serum online.

If you have mature skin

AHAs can help diminish the signs of aging by targeting fine lines and deeper wrinkles. They can also deal with roughness, leaving skin glowing.

Dr. Dennis Gross Skincare’s Alpha Beta Daily Peel contains a bunch of age-fighting antioxidants along with hydroxy acids.

Shop for Dr. Dennis Gross Skincare’s Alpha Beta Daily Peel online.

If you have hyperpigmentation or scarring

To reduce the visibility of dark marks and scars, use a BHA like salicylic acid that can encourage skin cell turnover or a strong AHA formula.

With a 5 percent glycolic acid content, Alpha-H’s Liquid Gold is designed to help pigmentation and hydrate skin.

Shop for Alpha-H’s Liquid Gold online.

If you have signs of sun damage

AHAs have been proven to be effective in reducing the appearance of sun damage, says King.

She recommends a combination of two acids — glycolic and lactic — adding that, together, they “resurface uneven texture and reduce surface pigmentation while supporting natural cell turnover.”

Omorovicza’s Acid Fix contains both.

Shop for Omorovicza’s Acid Fix online.

If you’re prone to ingrown hairs

Both lactic acid (an AHA) and salicylic acid (a BHA) can help stop those pesky ingrown hairs.

They do so by getting rid of dead skin, softening skin texture, and physically lifting ingrown hairs above the surface.

Try the Malin+Goetz Ingrown Hair Cream for extra calming properties.

Shop for Malin+Goetz Ingrown Hair Cream online.

There are two things you need to remember post-exfoliation: moisturizer and sun protection.

Chemical exfoliants do have the potential to leave skin feeling dry. To combat this, moisturize well immediately afterward.

You’ll also need to apply SPF, as AHAs and BHAs can make skin more sensitive to the sun.

In fact, if you’re planning on spending a day in the sun, it’s best to apply an exfoliating acid at night.

You can, but you probably don’t need to. For the average person, one acid is usually enough to get the job done.

This is especially true for people with sensitive skin or who are using retinoids.

But if your skin could benefit from a little extra help, there are a few rules to stick to.

Combining PHAs with AHAs or BHAs is generally OK. But, notes King, “You will lose the benefit of [PHAs] being more gentle.”

It’s also possible to mix AHAs and BHAs, but stick to a gentler AHA, such as lactic acid.

Test the combination on your skin before going full steam ahead. Try it once a week and use gentle cleansers and moisturizers alongside to keep skin hydrated.

If you’re mixing acids, use the thinnest texture first, advises King. However, “You don’t need to wait for one to absorb before applying the next.”

Thankfully, it’s easy to notice when you’re exfoliating too much or not enough.

Signs of under-exfoliation include a rough texture, dull complexion, and a feeling that your skin care products are no longer working due to a buildup of dead skin.

Over-exfoliation commonly takes the form of irritation, such as inflammation and dryness. You may also notice breakouts and peeling.

If you experience any of the above, stop exfoliating until your skin has fully healed.

As long as you listen to your skin, chemical exfoliation is an easy and effective way to get that coveted glow.

Remember to start slowly with a low concentration. If your skin’s happy, increase the frequency and strength until you achieve your desired result.

Lauren Sharkey is a journalist and author specializing in women’s issues. When she isn’t trying to discover a way to banish migraines, she can be found uncovering the answers to your lurking health questions. She has also written a book profiling young female activists across the globe and is currently building a community of such resisters. Catch her on Twitter.