What are acids, and do you need them in your skin care routine?

You’ve probably seen serums, cleansers and moisturizers showcasing active ingredients that can help reduce wrinkles, brighten skin or prevent breakouts.

These ingredients are typically acids — like salicylic acid, popular for treating acne, or ascorbic acid (vitamin C), often touted for its antioxidant properties.

But what exactly are “actives” and how do they work?

Basically, it’s “an ingredient that causes physiologic changes in one of the skin layers that is measurable both scientifically and visually,” Dr. Lisa Donofrio, a dermatologist who teaches at both Yale and Tulane universities, told TODAY Style in an email.

In other words, actives actually change the skin in some way, as opposed to just covering it up.

HOW DO ACIDS AND ACTIVES AFFECT THE SKIN?

Acids — which are often what people mean when they talk about active ingredients in skin care — can lower the pH levels of the skin.

“In the process of bringing the pH level down, it puts the skin into an acidic state,” Renee Rouleau, an esthetician whose clients include Demi Lovato and Emma Roberts, told TODAY Style. “It works to dissolve and digest dead skin cells. It kind of dissolves the glue that holds dry, expired cells together.”

Two of the most common types of acids in skin care are alpha hydroxy acids and beta hydroxy acids. AHAs are water-soluble compounds, and they are often used as exfoliants.

“Alpha hydroxy acids are by far probably the most common things we use in skin care to treat sun spots, pigmentation, to help with texture and tone in the skin, to help with fine lines,” Dr. Jennifer Chwalek, a dermatologist at Union Square Laser Dermatology in New York, told TODAY Style.

If you’ve never used exfoliating acids in your skin care regimen before, the key is to start slowly.

Common AHAs include glycolic acid, which can help with dryness and age spots, and lactic acid, which is great for gently exfoliating and hydrating sensitive skin.

Meanwhile, BHAs are oil-soluble, meaning they can penetrate clogged pores to deeply cleanse skin.

“They can really help with more oily skin and acne-prone skin,” Chwalek said. “It can help open up pores that get plugged up”

One of the best-known BHAs is salicylic acid, which is often used to treat acne.

CAN THEY CHANGE THE APPEARANCE OF YOUR SKIN?

Because acids change the skin on a chemical level, they often have a noticeable effect on the appearance of skin “by peeling off the outer skin layer, thus making the skin more luminous,” Donofrio said.

They can also reduce the visible effects of ultraviolet damage, decrease collagen degradation and help restore the skin barrier.

Rouleau said she often recommends acids to clients who are preparing for an event and need a way to quickly get that special “glow.”

“The nice thing about an acid is that there’s immediate results,” she said. “You can use an acid … for smoothing, making pores look smaller, for removing surface dryness. They’re good for making the skin looker brighter and more light reflective. They also help to correct breakouts (and) smooth bumps.”

HOW TO USE ACIDS AND ACTIVES

There’s a dizzying array of acids and other actives on the market. Some require prescriptions, while others are available in over-the-counter serums, cleansers and toners in varying concentrations.

If you’ve never used exfoliating acids in your skin care regimen before, the key is to start slowly.

“I would start with an acid maybe twice a week, like maybe every three nights … just to see how your skin does with it,” Rouleau said. “Sometimes it can be a little strong or sometimes they’re just right, so I think taking it slow is always best. But you never want to apply it every day.”

The order of using acids and actives depends on the product. For some AHA-based products, like glycolic or lactic acid washes, Chwalek recommends cleansing with them first and then applying serums or other products.

Or, if you’re using a pad medicated with a certain acid, she recommends first washing your face with a gentle cleanser and then using the pad.

Serums containing acids should also be used after cleansing.

“Cleanse, tone, leave the toner damp, and apply (the serum) to the skin,” Rouleau recommended.

ARE THERE ANY RISKS?

Products with AHAs can cause skin irritation.

“It can create some redness and burning or flaking after you use it,” Chwalek said. “It all depends on the acid that you’re using and the concentration that you’re using it at.”

Lactic acid could be a good option for people with especially sensitive skin because it’s one of the most hydrating AHAs. Or, look for fatty acids like linoleic or oleic acid (which are not AHAs) that hydrate the skin and strengthen the skin’s natural barrier.

Acid-based products can also increase the skin’s sensitivity to the sun.

“You’re essentially exfoliating the skin, so it’s taking off the top layer of the skin, potentially,” Chwalek said. “So you really want to moisturize well and use really good sunscreen.”

Also, Chwalek notes that people with darker and/or sensitive skin should take extra care when using certain acids.

“If you’re too aggressive with an acid in a darker-skinned person, then you can create irritation and that may actually create hyperpigmentation or dark spots,” she said.

In general, it’s best to consult a dermatologist or esthetician about what acids and actives are best for you, depending on the results you’re trying to achieve.

“There might be other products that are better suited,” Chwalek said. “There might be ways of adding a little of this to your regimen that will be less irritating than doing something really aggressive.”

Donofrio also cautions that many acids available online aren’t always regulated by the Food and Drug Administration, so “stick to brands or formulations recommended by your dermatologist or ones that are available in major pharmacy chains.”

Here’s a guide to some of the most common acids and active ingredients found in skin care products:

AHAS

Alpha hydroxy acids are water-soluble molecules that are often derived from natural substances like fruit or dairy. They work in different ways depending on the acid, but in general, they exfoliate and smooth the skin, and can help reduce fine lines and hyperpigmentation.

In skin care products, AHAs are often combined with BHAs, another common category of acid.

SkinCeuticals LHA Cleanser Gel, $40, Dermstore

SkinCeuticals LHA Cleanser Gel

$40.00

$41.00

Dr. Tiffany Jow Libby, a dermatologist at Medical Dermatology and Cosmetic Surgery in New York City, swears by this LHA cleanser gel from SkinCeuticals. It combines two common AHAs, lactic and glycolic acid, with a popular BHA, salicylic acid.

“It comes in a huge bottle so I like it for patients who have acne on their chest and back,” Libby said. “They can use it in the shower and leave it one for a few minutes while you lather it up, so it almost acts like a mini-peel, and that big bottle will go a long way.”

BHAS

Beta hydroxy acids are oil-soluble molecules that can penetrate deeply into pores and oil glands to help with oily skin and acne.

Dr. Dennis Gross Alpha Beta Universal Daily Peel, $145, Amazon

Dr. Dennis Gross Alpha Beta Universal Daily Peel

$145.00

$150.00

$150.00

Libby is a fan of this alpha-beta peel from Dr. Dennis Gross, which combines glycolic, lactic, mandelic and other acids. However, it’s “a little intense,” she warns, so it may not be suitable for people with more sensitive skin.

SALICYLIC ACID

This is one of the most common types of BHA, and it’s commonly used as an acne treatment.

“Of all the acids, it’s the one that gets into the pore lining the best, and to help encourage the pore from getting clogged, which then leads to a breakout,” Rouleau said.

Libby recommends Neutrogena’s oil-free acne wash as an affordable product containing salicylic acid.

Neutrogena Oil-Free Salicylic Acid Acne Fighting Facial Cleanser, $20 (Pack of 3), Amazon

Neutrogena Oil-Free Salicylic Acid Acne Fighting Facial Cleanser

$20.01
$24.02

$6.67

$6.49

“I really like it for my acne-prone patients. It’s really gentle and it clears out the pores,” she told TODAY. “Salicylic acid is attracted to oil glands, so it gets a little deeper in the pores, so it helps to remove that excess sebum, too.”

Another one of Libby’s favorite products containing salicylic acid is this Glytone acne treatment spray.

Glytone Acne Treatment Spray, $42, Amazon

Glytone Acne Treatment Spray

$42.00

$42.00

“The reason I like it is the applicator. It’s a spray bottle … for people who have acne on their back,” she said. “We’re giving them these creams to take home and they can’t even apply them to themselves over a large surface area. But this is a spray so they can spray it on their back, or even after the gym, they can wipe down and spray.”

GLYCOLIC ACID

This is one of the most commonly used AHAs. It’s especially good for removing dead skin cells to reduce dryness. It’s also effective in treating pigmentation and discoloration, age spots and post-breakout marks, Rouleau says.

When it comes to products featuring glycolic acid, Libby is a fan of this Glytone Enhance Brightening Complex, an exfoliating and moisturizing cream that is great for dealing with pigmentation issues.

Glytone Enhance Brightening Complex with Azelaic & Glycolic Acids, $74, Amazon

Glytone Enhance Brightening Complex with Azelaic & Glycolic Acids

$74.00

$74.00

It’s especially helpful for women who are pregnant.

“When you’re pregnant you get acne, you get pigmentation problems that arise because of your hormones being in flux,” Libby said. “There’s not really much we can give patients during pregnancy, but glycolic acid and azeleic are both safe in pregnancy so it’s great.”

Libby also loves these facial radiance pads from First Aid Beauty.

First Aid Beauty Facial Radiance Pads, $32, Sephora

First Aid Beauty Facial Radiance Pads

$32.00

$32.00

$32.00

“Those are just glycolic acid as well so they’re great to just to slightly wipe over your face and use daily as a gentle exfoliant,” she said.

HYALURONIC ACID

Hyaluronic acid occurs naturally in the human body and is found in younger people’s skin and connective tissues, according to the Cleveland Clinic. As we age, our natural hyaluronic levels tend to decrease. It’s often used in skin care products to reduce wrinkles.

Phyto-C Hyper Hydrate, $55, Phyto-C

Phyto-C Hyper Hydrate

$55.00

Libby swears by hyaluronic acid in general, and she loves this hydrating serum from Phyto-C.

“It’s a really concentrated form of hyaluronic acid, which is great for moisturizing the skin,” she said. “It’s a highly moisturizing serum and I like to apply that directly to my skin, or you can mix it in with a moisturizer in the dryer winter months. But I like using it all year round as a great, light moisturizer.”

Neutrogena Hydro Boost Hyaluronic Acid Gel-Cream, $17 (usually $19), Amazon

Neutrogena Hydro Boost Hyaluronic Acid Gel-Cream

$16.97
$18.98

$16.97
$17.97

$16.99

She also recommends the Neutrogena Hydro Boost gel cream, which is available over the counter at the drugstore.

“It’s a gel cream and it has a really nice, light texture, goes on lightly,” she said. “I find it very hydrating. I use it in the winter time when you need a slightly thicker moisturizer, but it’s not too greasy for the summer, either.”

LACTIC ACID

Lactic acid is an AHA that is especially good for people with sensitive skin.

“Lactic acid is the most hydrating of all the acids, so oftentimes it’s used for sensitive skin that has kind of a more delicate skin barrier and therefore needs more hydration in the skin,” Rouleau said.

When it comes to products containing lactic acid, Libby recommends an affordable daily moisturizer from AmLactin.

AmLactin Daily Moisturizing Body Lotion, $13 (usually $16), Amazon

AmLactin Daily Moisturizing Body Lotion

$12.49
$15.99

$22.49

$12.79

“It’s for a larger body surface area … if you wanted to do a little gentle exfoliation but use it all over,” she said. “That’s one we often recommend to patients for … those stubborn bumps … or even to help remove the top layer of dead skin.”

L-ASCORBIC ACID

L-ascorbic acid (aka vitamin C) is an antioxidant that can stimulate collagen production and minimize wrinkles, according to the Cleveland Clinic. It’s not an exfoliant but it’s still acidic on the skin, so check with a dermatologist before using it in combination with other acids.

Libby recommends this serum from Revision that contains a high concentration of vitamin C.

Revision Skincare Vitamin C Lotion 30%, $77, Walmart

Revision Skincare Vitamin C Lotion 30%

$77.30

$119.00

“It goes on really nicely. I use that every day,” she said. “Basically, it’s really high penetration so it really gets into the skin very well. It’s a very light moisturizing serum.”

CITRIC ACID

Citric acid is another nonexfoliating AHA. It’s sometimes used as a pH-adjuster in skin care products.

Exuviance Daily Resurfacing Peel CA10, $65, Ulta

Exuviance Daily Resurfacing Peel CA10

$65.00

$65.00

Chwalek personally uses this Exuviance peel with citric acid, along with a glycolic foaming cleanser, and she definitely recommends it.

“I swear my skin always looks better after,” she said. “The texture is smoother and it looks more radiant.”

AZELAIC ACID

This type of acid is often found in prescription-strength acne creams and gels. It kills bacteria that cause acne and helps clean the pores, according to the Mayo Clinic.

The Ordinary Azelaic Acid Suspension 10%, $8, Sephora

The Ordinary Azelaic Acid Suspension 10%

$7.90

Libby recommends this brightening formula from The Ordinary.

“It’s safe in pregnancy and it’s great for evening out pigmentation,” she said. “It’s good for sensitive skin, good for rosacea.”

LINOLEIC ACID

Linoleic acid is an essential fatty acid that helps strengthen the very top layer of the skin, Chwalek says. Linoleic acid is essential for making ceramides, a kind of fatty molecule that’s a key part of the skin barrier.

Dr. Dennis Gross Skincare Clinical Concentrate Radiance Booster, $68, Sephora

Dr. Dennis Gross Skincare Clinical Concentrate Radiance Booster

$68.00

$68.00

$68.00

Libby is a fan of this radiance booster from Dr. Dennis Gross.

“It’s a really popular one. It’s great for back acne,” she said. “It’s really good for gentle exfoliation but still slightly hydrating as well.”

FERULIC ACID

Ferulic acid is a plant-based acid with antioxidant properties. It’s often used in combination with vitamin C or vitamin E to help with wrinkles and sun damage.

SkinCeuticals C E Ferulic, $175, Amazon

SkinCeuticals C E Ferulic

$175.00

$166.00

$166.00

Libby recommends this SkinCeuticals serum that contains ferulic acid and vitamins C and E.

“It’s one that a lot of dermatologists will always recommend,” she said. “It’s one of the most stable formulations of vitamin C, but I will recommend it more to my patients who are not acne prone, because I think it tends to make you break out a little.”

MANDELIC ACID

Mandelic acid is an AHA that is derived from bitter almonds. It can help reduce the appearance of wrinkles, hyperpigmentation and acne.

Vivant Skin Care 8% Mandelic Acid 3-in-1 Serum, $60, Amazon

Vivant Skin Care 8% Mandelic Acid 3-in-1 Serum

$60.00

$60.00

Chwalek says this Vivant toner is “great for oily, acne-prone skin.”

“It can help to control oil production and the mandelic acid also can help hyperpigmentation,” she said.

OLEIC ACID

Similar to linoleic acid, oleic acid is a fatty acid that works as a “building block” for the skin barrier. Oleic acid helps the skin produce its natural oil barrier and helps with hydration, Chwalek says.

DHC Olive Concentrated Cleansing Oil, $31, Amazon

DHC Olive Concentrated Cleansing Oil

$31.00

$31.00

Chwalek is a fan of cleansing oils like this one for hydrating dry skin, especially in winter.

“This one contains antioxidants and is naturally formulated (free of parabens, fragrance, color, phthalates),” she said.

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