You might have heard that makeup has a shelf life, but do you actually follow these guidelines? If you're like many other cosmetics users, probably not. In fact, nearly 98% of participants in one study said that they've worn makeup past its expiration date. 

While some people may use expired makeup to save money or avoid waste, others simply don't realize that their products should be thrown away after a certain point. Either way, there are potential health risks of using cosmetics after they've hit their expiration date. Not only does it increase your risk of eye and skin irritation, but it can also make you more likely to develop an infection.

To avoid these complications, it's important to practice good makeup hygiene. Here's how to do that.

When does eye makeup expire?

Most eye makeup has a shorter shelf life than other types of cosmetics, like blush and foundation. That's because using liquid-based products (like mascara and liquid eyeliner) around your eyes makes it easier to spread bacteria, which can lead to eye infections, per Mayo Clinic.

Here's how long different kinds of eye makeup typically last: 

• Mascara: Three months
• Liquid eyeliner: Three months
• Pencil eyeliner: One to two years
• Powder eyeshadow: Two years
• Cream eyeshadow: One year

In the US, cosmetics aren't required to have expiration dates printed on their labels, but many do. Here's how to find them.

First, look at the label on your product. If you see an open jar icon (known as the Period After Opening, or PAO, symbol) with a number printed inside, that will help you determine the shelf life of the cosmetic. For example, if there's a 12 listed, the product is safe to use for a year after you've opened it. If there's a 24, the makeup is good for up to two years.

If you don't see the PAO symbol, you can use the recommendations above to determine how long you can use the product before it expires.

3 risks of wearing old eye makeup

Whether it's mascara, eyeliner or eyeshadow, wearing old eye makeup comes with certain risks. Here are some of the potential dangers of using expired makeup products.

Irritation

Once makeup passes its expiration date, several things can happen. For one, the ingredients can start to go bad. If this happens and you keep using the makeup, these spoiled ingredients could get into your eye and cause redness or irritation.

Over time, makeup products and tools can also start to harbor bacteria and fungi, which they pick up from your eyelashes, eyelids or fingers. If you continue using these contaminated cosmetics, you could end up with skin irritation or breakouts.

Infections

By wearing out-of-date eye makeup, you also raise your risk of developing certain infections, some of which can be serious. In fact, according to the Food and Drug Administration, people have been temporarily or permanently blinded after getting an infection from their eye makeup.

Sharing makeup with others also increases your chance of developing an eye infection, like conjunctivitis (also known as pink eye). So if you borrow your friend's mascara, and they unknowingly have an infection, they could pass it on to you. Signs of an eye infection include pain, redness, discharge, swelling and inflammation. If you have any of these symptoms, reach out to your doctor.

Scratches

When you're putting on makeup, there's always the possibility of accidentally bumping or scratching your eye, especially if you're rushing or applying makeup on the bus or in the car. It might not seem like a big deal in the moment, but this can have serious consequences if the makeup is expired and has bacteria buildup.

Whether it's with a mascara wand, eyeliner pencil or your finger, scratching your eye while putting on makeup can lead to a corneal abrasion and, potentially, an infection, according to the UIC College of Medicine. These are painful injuries that can compromise your vision and require medical attention.

How to practice good eye makeup hygiene

With proper eye makeup hygiene, you can reduce your risk of irritation, infection and other health issues. Here are some tips to keep your eyes healthy when applying makeup.

• Throw away spoiled or expired makeup. It may be tempting to hang onto your favorite liquid eyeliner until it runs out, but once it expires, it's time to get rid of it. If not, you're putting your eye health on the line. You should also toss any makeup that's changed color or smell.
• Don't try to revive dried-out products. If you have a dried-out tube of mascara, don't add water or saliva to try to rehydrate it. Doing this can introduce bacteria into the container, which can transfer onto your eyes when you use the product, Ohio State University reports.
• Wash your hands before applying makeup. When your hands are clean, you're less likely to transfer bacteria from your fingers to your face.
• Store makeup properly. Cosmetics can break down faster when exposed to high heat and moisture. To extend their shelf life, it's best to leave your makeup products in a cool, dark area.
• Remove makeup thoroughly. Going to sleep with makeup on can clog your pores, make you break out, and worsen any skin conditions you already have. If you don't cleanse your eye area, you could also end up with eyelid dermatitis or a sty, as Everyday Health reported.
• Avoid "tester" products at cosmetics stores. As we've mentioned, sharing eye makeup can spread bacteria and infections from person to person. Just like you shouldn't share cosmetics with your friends, you should also avoid using testers or sample products in makeup stores.
• Take precautions during and after an eye infection. If your eyes become infected, stop wearing makeup in your eye area. You should also throw out any cosmetics that you'd been using when you got the infection.
• Don't use other types of makeup around your eyes. You might have seen people using lip liner as eyeliner, but there are good reasons not to do this. For one, you could introduce bacteria from your mouth into your eyes. But also, lip products might contain additives that aren't approved for use around your eyes.