Medically reviewed by Katelyn Hagerty, FNP
Written by Our Editorial Team
Last updated 1/25/2022
That spoiled milk in the back of your fridge? Turns out, it may be really great for your skin. Well, kind of.
Sour milk contains lactic acid — which has some pretty big skin benefits. So much so that many skin care brands incorporate it into things like serums, moisturizers and face washes.
But lactic acid has a unique set of characteristics that can really help your complexion.
To find out exactly what lactic acid is and how adding it to your skincare routine can benefit your complexion, keep reading.
Lactic acid is actually found in a number of foods and dairy products. We’ve already mentioned sour milk, but it can also be found in yogurt, sauerkraut and other fermented foods.
Other AHAs that are sometimes found in skin care products are citric acid, hydroxycaprylic acid and hydroxycapric acid.
Generally speaking, lactic acid (and other AHAs) exfoliate your top layer of skin — or cause the shedding of surface skin.
The Food and Drug Administration (FDA) has found that the use of AHAs like lactic acid is safe to use in skin care products.
So, why would someone want to use lactic acid products on their face?
There are a number of reasons, really. Here are some of the most prevalent benefits of using skin care products that contain this type of acid:
Refresh your complexion. Who doesn’t want fresher, brighter skin? Lactic acid increases the rate of cell turnover and renewal (this is the process where your skin sheds dead cells and replaces them with new ones). The result? A brighter complexion.
Say “hello!” to hydration. This ingredient can also help boost skin moisture and improve the skin barrier (a natural protectant your skin has to keep moisture in).
The benefits of lactic acid sound pretty great, right? But before you dive into using it, you should brief yourself on some of the potential side effects.
This way, you know what to be on the lookout for if you’re using it.
The primary thing you may notice when you use products with lactic acid is that your skin becomes more sensitive to the sun. Research suggests that this sensitivity can last up to a week after you’ve stopped using products with AHAs like lactic acid.
The reason your skin may be more sensitive to the sun is because lactic acid exfoliates away dead skin cells, leaving you with new skin that’s more prone to being burnt by those UV rays.
Given this, it’s important to protect your skin anytime you're in the sun. Heck, you should be protecting your skin regardless of whether or not lactic acid products are part of your skin care routine. As we all know, sun-damaged skin sucks.
The American Academy of Dermatology recommends selecting a sunscreen that is labeled broad-spectrum — this means that it protects you from UVA and UVB rays. You also want to make sure you reach for something with an SPF 30 or higher.
In addition to sun sensitivity, people who use a lactic acid product may experience irritation. This can show up as redness, itchiness, swelling, dryness or burning. This may be especially true if you have sensitive skin to start with.
If you experience any of these things, it would be wise to schedule a consultation with a healthcare professional.
Want brighter skin? How about less blemishes and a healthy glow? A better question would be, “Who doesn’t want these things?!”
Lactic acid may just be the answer — or one of them, at least.
It’s one of the more popular alpha hydroxy acids used in skin care products — the other one often used is glycolic acid.
That’s because this skin care ingredient can help slough away dead skin cells to improve skin texture, uncovering fresher, brighter skin underneath.
Potential side effects of using lactic acid are sun sensitivity and potential skin irritation. Though, you should know that not everyone who uses products with this AHA will experience these side effects.
If you’d like an expert opinion on whether your complexion could benefit from using something like a lactic acid serum or moisturizer, make an appointment with a healthcare professional. If you have sensitive skin, it’s also a good idea to chat with a pro before you start using something new.