What Happens to Your Face When You Use Expired Makeup ... It’s not pretty.

You know you’ve done it—we're talking about using a makeup product that's way past its expiration date. After all, you shelled out major dough for that mascara, so why would you want to toss it once the date on the tube has come and gone?

But expiration dates serve a bigger purpose than merely getting you to buy another product. That’s because old makeup not only works less efficiently—it can do major damage to your skin. You’ve been warned, ladies.

What Happens to Makeup When It Expires
"The consistency of the product is going to change over time," says Hadley King, M.D., the dermatologist at SKINNEY Medspa in New York City. "They're going to dry out, get clumpy and not apply as smoothly. That's true for everything from mascara to lipstick and foundation."

The efficiency of active ingredients also becomes compromised over time. "For example, after a foundation with SPF has expired, the sun protection may not be as strong as it was when fresh," says King. This also applies to products that include salicylic acid for acne prevention or retinol to prevent fine lines. 

What Happens to Your Skin When You Use Expired Makeup
Now here's the real danger. "All of the molecules in these products can break down into something else, and you can have a reaction to it," says King, who goes on to explain that if you experience irritation in response to the molecule breakdown, it could lead to inflammation. And contact dermatitis, a broad term for inflammation of the skin, can in turn lead to redness, bumps, a rash, or even blisters and swelling of the skin, says King. Um, that doesn't sound good, does it?

Your expired makeup can also start to harbor bacteria. When it comes to your skin, this can mean irritation and bumps that look like acne. And when it comes to your eyes, this bacteria buildup can actually cause infections and pink eye, says King. As for lipstick, using an expired one can cause swelling. So as a general rule, you should replace your mascara every three months, eyeliner and eye shadow every six to 12 months, and lipstick every one and a half years. Meanwhile, the average expiration date for foundation, powder, and other facial makeup is 12 months.