Derms Say Lactic Acid Can Significantly Reduce Breakouts and Fine Lines

If someone told you that applying spoiled milk to your skin could get rid of blemishes and diminish fine lines, would you believe them? While it sounds like a too-good-to-be-true Pinterest hack, the science serves as proof. Lactic acid—an exfoliating acid found in sour milk—can help you achieve softer, smoother skin.

The use of lactic acid dates back to Ancient Egypt, and these days, beauty brands have caught on and begun to isolate lactic acid, integrating it into serums and cleansers for the consumers' benefit. Dhaval Bhanusali of Hudson Dermatology & Laser Surgery explains that lactic acid is now known as "One of the more common alpha hydroxy acids," adding that it's "used to improve skin tone and texture as well as lightly exfoliate the skin."

We consulted Bhanusali and other experts for a full perspective on how lactic acid can benefit the skin.

What Is Lactic Acid?

Swedish chemist Carl Wilhelm Scheele was the first to isolate the compound from sour milk. In the late 1800s, German pharmacist Boehringer Ingelheim uncovered how to mass-produce lactic acid when he realized it was a byproduct of fermented sugar and starch in sour milk via bacteria. "Lactic acid is a light peeling agent, depending on strength," says MacGregor. She also notes that it "can smooth out the skin, making it glow." You can find lactic acid in many of the same places other Alpha Hydroxy Acids (AHAs) are found, including products that advertise that they contain AHAs but don't specify which they contain.

Benefits of Lactic Acid

• Kills bacteria: Research around lactic acid's efficacies as they relate to the skin are limited in the early to mid-1900s, but in 1985, a study found that lactic acid helped to kill skin infections in newborn infants. It tracks that it would do the same in adults, including the irritating, acne-causing kind.
• Diminishes wrinkles: Later, in '96, when different concentrations were tested (5 percent and 12 percent), researchers observed that a higher concentration penetrated both the dermis and epidermis (5 percent could only reach the epidermis) for firmer, thicker skin, resulting in fewer fine lines and wrinkles.
• Reduces acne: It's also been proven to reduce acne lesions. So yeah, you could say it's a bit of a hero ingredient.
• Increases cell turnover: According to Schep, lactic acid "works by increasing the rate of skin turnover, causing new and younger-looking skin to grow."
• Helps skin hold moisture: Similarly, Schep says that "The new skin may also have better moisture-holding capability."

Lactic Acid vs. Other Acids

If you're wondering how it differs from other acids, like, say, glycolic acid, the lactic acid molecule is actually larger, so it can't penetrate as deeply—instead, you're getting more surface treatment (polishing, firming, exfoliating goodness). This is good news for those with sensitive skin, though, who'll likely be able to tolerate its effects better. This isn't just good news for people with sensitive skin, though, because it means lactic acid is also less likely than glycolic or salicylic acid to cause irritation and disrupt the pH of your skin barrier. So pretty much anyone can use it. If you're someone with acne-prone skin and need a lot of exfoliation, you can alternate your use of lactic acid with the use of something deeper like salicylic, which will clear off dead skin and deep clean your pores.

Side Effects of Lactic Acid

As with any acid, it's important to use it wisely. "Do not use on irritated or red skin," MacGregor warns. Using too much of any one acid too often can lead to inflammation, which accelerates the aging process. Using too much at once can also lead to inflammation or—worse—rashes and chemical burns. It is worth noting that lactic acid irritates the skin less than many other acids and, therefore, can be used more often than something like (the very intense) salicylic acid.

How to Use It

Celebrity esthetician Renée Rouleau recommends incorporating a lactic acid product (like a serum or toner) on a three-on/three-off schedule, i.e., you should apply the acid for three nights in a row, then take a break for three nights to treat your skin with hydrating ingredients that nourish the new cells you've revealed.

How Not to Use It

You should consider discontinuing strong exfoliating products such as retinoids or scrubs when regularly using lactic acid (or any acid). "As it makes new skin grow, which may not have any pigment in it, it may cause increased susceptibility to sunburn. Therefore, it is often formulated with sunscreen," says Schep. Since sloughing off layers of your skin also makes you more prone to sun damage, apply an SPF of at least 30 daily (as you should be, anyway!).

The Final Takeaway

When used with frequency, lactic acid can have a serious impact. It can help kill bacteria on the skin, diminish wrinkles, reduce acne, increase skin cell turnover, and help your skin hold moisture. Plus, it's an ideal exfoliating acid for most skin types as it's less irritating than glycolic or salicylic acid. Just remember not to overdo it—you can typically use it up to three times per week—and wear sunscreen to avoid sun damage.