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If there's spoiled milk in your fridge, you're already a step ahead.

When it comes to all-star skincare ingredients, science has a way of creating masterpieces straight from Mother Nature. Take lactic acid, for instance: it's an acid that's naturally present in dairy products and can be extracted and used as an exfoliant when products like milk go bad. This isn't to say that you should leave your milk in the fridge and douse your skin in it once it expires (gross). Cosmetic scientists have already done all that hard work for you by incorporating lactic acid into serums and cleansers that provide significant skin benefits. If you want smoother, more radiant skin, lactic acid is definitely going to be your new bestie.

Lactic acid has a reputation for being one of the gentler alpha hydroxy acids, but it's also known for its ability to help reduce sun damage, signs of aging, and dullness when used on a regular basis. One of the reasons the beauty world is raving about its effects is because it can improve the skin's natural ability to retain moisture, a benefit that other acids in the category typically don't provide.

Although the powerful exfoliant will undoubtedly aid in the reduction of uneven skin texture, acids can be tricky. It’s highly recommended that you combine lactic acid with sunscreen since the peeling of dead skin cells can make you more susceptible to sun damage.

To learn more about lactic acid, what its benefits are, and how to incorporate it into your own skincare routine, read on.

According to Dr. Mack, lactic acid is not only beneficial if you deal with acne and discoloration, it's also recommend for people who have sensitive skin but typically deal with irritation from other exfoliating acids. "It's not as irritating as other AHAs and BHAs like glycolic and salicylic acids," she says.

Though lactic acid is a gentle exfoliant that works well on sensitive skin, it can cause rashes as a result of irritation if used too often. Dr. Mack suggests using it every other day when initially adding it to your skincare routine."Without causing irritation, this frequency may be sufficient to achieve the desired results," she says. If you're using a lactic acid-based product, you shouldn't use any other exfoliants on your skin. This also goes for vitamin A derivatives like over-the-counter retinols or prescription-strength retinoids, benzoyl peroxide, and other alpha and beta hydroxy acids.

Once your skin has gotten used to it, lactic acid should only be used once per day on the skin. "To reduce the risk of photosensitivity, I recommend applying it at night," Dr. Mack says. "If you have other exfoliators in your skincare routine, don't use them on the same night as your lactic acid product." Because lactic acid is well-tolerated, you can use it twice a week with another hydrating topical (e.g., one with hyaluronic acid).

Ready to try it out? Try adding a few of this lactic acid-containing products to your skincare routine.

Packed with 9% lactic acid, this fan-favorite gently exfoliates the skin’s epidermal layer, visibly reducing pigmentation and evening the complexion. It also contains hyaluronic acid to help minimize the risk of over-drying and irritation.

Lactic and glycolic acids team up in this product that can be used to minimize hyperpigmentation and even out the complexion.

This serum contains lactic acid as well as other natural brighteners like licorice root extract to reveal a more even, brighter complexion.

Those who have keratosis pilaris (characterized by a bumpy, rough texture found most commonly on the arms, buttocks and thighs) will benefit from this scrub. It has both physical and chemical exfoliants to smooth the skin and reduce the appearance of bumps.

Think of this as the fountain of youth in a bottle. It's a super-powered, milky serum that's lightweight (but powerful!), hydrating, and calming. The botanically rich ingredients soften, soothe, and balance the skin while also helping to safeguard against harmful blue light rays and free radicals.

With its formula that includes lactic, citric, malic, and tartaric acids, this essence reduces the appearance of pigmentation and minimizes the appearance of fine lines and wrinkles. The result? A luminous glow, boosted hydration, and increased brightness.

Dr. Mack often recommends this one for her patients, as it can be used on dry, discolored, bumpy skin, and can be prescribed or bought over-the-counter.