Lactic acid is gentle, yet effective. (Promise!)

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Why You Need This Exfoliating Acid in Your Routine
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Using expired sour milk on your face probably seems like a recipe made in TikTok hell, but lactic acid is actually a chemical exfoliant that's gentle enough to treat acne and uneven texture on sensitive skin.

Luckily, there's no need to play around with the spoiled jug of milk that's been in the back of your fridge for months. Beauty brands have long been onto the benefits of lactic acid, safely incorporating it into their serums, creams, and masks.

But before you add any lactic acid products to your cart, we turned to a top dermatologist and chemist to get a full breakdown on what the chemical exfoliant does for your skin and the best methods for incorporating it into your routine.

How Does Using Lactic Acid Benefit Your Skin?

Lactic acid is an exfoliating alpha hydroxy acid (AHA) that is found naturally in milk, but it can also be produced synthetically in a lab.

"Acids can remove several layers of dead skin in just one treatment allowing treatment products and skincare to effectively penetrate the skin," says Dr. Michele Green, a board-certified cosmetic dermatologist in New York City. "They can remove blemishes, fade sunspots, improve skin tone, texture, reduce hyperpigmentation and superficial wrinkles."

In the case of lactic acid, it can be used as both an anti-aging and acne treatment because it exfoliates, improves fine lines and wrinkles, and improves the appearance of discoloration.

Michelle Wong, cosmetic chemist and founder of Lab Muffin points out that while lactic acid is an exfoliant, it's also a hydrating humectant. "It can hydrate your skin, reduce clogged pores, smooth out skin texture and help fade pigment," she says.

Who Should Use Lactic Acid?

For sensitive skin types, lactic acid can be a great chemical exfoliant because it's gentler than other AHA and BHA acid.

"Lactic acid is best used on sensitive skin because it is a mild exfoliant which will not disrupt the pH of the skin or cause redness and irritation," Dr. Green says.

Because lactic acid has a larger molecule size in comparison to other AHA acids, it doesn't penetrate the skin as deeply, providing a more superficial exfoliation. In other words, lactic acid isn't as potent, but it can still be effective, which is ideal for sensitive skin types that are prone to irritation.

What Ingredients Don't Play Nice With Lactic Acid?

"Lactic acid should not be used in conjunction with other forms of AHA’s or in addition to using BHA’s, retinols or tretinoin," Dr. Green shares. "These ingredients all cause cell turnover and some degree of exfoliation. When combined together, they can cause severe skin irritation."

Wong says that because lactic acid products are at a low pH, they can conflict with pH-sensitive ingredients such as peptides. "Usually it’s not a big problem if you wait 15 minutes between applying products," she says.

How Should You Use Lactic Acid in Your Skincare Routine

There are a number of products infused with lactic acid, from cleansers to serums to face masks. While which one you try is up to you, it's always best to consult with a dermatologist if you're unsure about adding anything new to your existing routine.

Just don't forget to apply SPF every morning, because like other exfoliants, lactic acid can cause sun sensitivity.

"Lactic acid is also a melanin suppressor therefore it inhibits tyrosinase which is the enzyme responsible for melanin production," Dr. Green says. "Because it decreases your melanin production, you should wear sunscreen and protective clothing to protect the treated areas from sun damage."

Due to this reduction in melanin production, Dr. Green says the skin is "noticeably healthier, lighter, and brighter almost immediately."

VIDEO: When You Apply Sunscreen in Your Skincare Routine Actually Matters A Lot

The 5 Best Lactic Acid Products

Philosophy Renewed Hope in A Jar Facial Moisturizer

Lactic Acid Skincare Products
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Dr. Green is a fan of Philosophy's classic moisturizer because it's lightweight and filled with lactic acid and antioxidants. Bonus: the updated formula now contains SPF 30 protection to help streamline your routine.

To shop: $39; sephora.com

Sunday Riley Good Genes  All-In-One Lactic Acid Treatment

Lactic Acid Skincare Products
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Along with the rest of the internet, Dr. Green sings the praises of Sunday Riley's cult-favorite lactic acid-powered serum. "This product is great, containing both lactic acid and licorice, which work great for anti-aging and hyperpigmentation."

To shop: $85; sephora.com

Dermalogica Skin Resurfacing Lactic Acid Cleanser

Lactic Acid Skincare Products
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This cleanser gently exfoliates skin while simultaneously nourishing it, thanks to a blend of vitamin E and rose flower oil.

To shop: $45; sephora.com

SkinCeuticals Clarifying Clay Mask

Lactic Acid Skincare Products
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While clay masks are great at sucking excess oil from your pores, they also notoriously drying. That's why in addition to adding a 2% exfoliating acid blend to its mask, SkinCeuticals has also included a mix of soothing ingredients such aloe and chamomile to keep skin soft and supple.

To shop: $55; dermstore.com

The Ordinary Lactic Acid 10% + HA

Lactic Acid Skincare Products
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For anyone looking to experience lactic acid for the first time without spending too much coin, The Ordinary's serum is your best bet. In addition to 10% lactic acid, it contains smoothing hyaluronic acid to give skin a hydrated, plump look and Tasmanian pepperberry to offset potential irritation.

To shop: $7; sephora.com