Are you someone who takes expiration dates for their word? Or did you grow up being taught that those dates are mere suggestions? Whatever the case may be, one thing’s for sure: When it comes to expired beauty products, experts say that the dates matter. And if you don’t believe that—and continue to use a product past its best-by date—there’s a very real chance your skin will show it.

Unlike food, beauty products that are past their expiration date won’t make you physically ill, however, they can potentially wreak havoc on your complexion. Keep reading for what you need to know

What happens to your skin when you use an expired product

Skin-care and makeup products expire due to the active ingredients they’re formulated with, explains Nada Ward, the founder of solid soap company Beauty Kin.“These kinds of ingredients can encourage faster bacteria growth which, if applied to the face, can cause reactions such as irritation or redness,” she says.

Additionally, Erum Ilyas, MD, a board-certified dermatologist at Schweiger Dermatology Group in King of Prussia, PA, says that bacteria can work their way into a container simply by being exposed to air (which explains why most products’ expiration dates are based on when you opened them, not on when they were formulated).

Even if a product doesn’t become a cesspool for bacteria, once it’s past its expiration date it likely won’t work as well as it once did.  “[Expiration dates] are based on manufacturers demonstrating the stability of the product,” Ilyas explains. “Beyond these dates, it is difficult to say if the product will be able to fulfill its claims. Although unlikely for the product to cause harm, the reality is that it may lose potency over time.”

In other words, if you want your skin care to actually do something for your skin (which, let’s be honest, most of us do), it’s best to toss your expired products. While using them won’t technically do any harm, they won’t do any good, either.

How strictly should you adhere to beauty product expiration dates?

On most beauty packaging, you’ll find a small picture of a jar with a number in it, which indicates how many months the product will last after you open it (usually 6, 12, 18, or 24, depending on the formulation). However, according to Ilyas, these “best by” dates may not be totally foolproof.

“The preservatives within most products are meant to reduce the risks associated with these microbes,” she says. “However, given the fact that beauty products often come into contact with facial skin or sensitive areas such as eyelids and lips, it is recommended to toss products at the 90-day mark after breaking the seal.” Keep an eye on how your product looks: if you notice separation in the ingredients, a drastic color change, or a funky smell, it’s a good sign that it’s gone bad.

All of that said, there is one type of skin-care product that you should always toss once its “best by” date has passed. “The most consequential [product] in this category could be expired sunscreen,” says Ilyas. “With expired sunscreen use, there is a risk of decreased effectiveness and a false sense of security when exposed to UV.”

The good news is that because sunscreens are considered an OTC drug, they all come with a very clear expiration date on their packaging, so you’ll know full well when it’s time to say goodbye.

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