Hands up if you keep your makeup products so long that you don’t remember when you bought them? Does it pain you to throw away anything that’s not completely empty?

Out of date make-up products have been found to contain unsafe levels of potentially harmful bacteria in a series of tests conducted at the London Metropolitan University. According to a study by the university, five products sent in by UK beauty consumers were tested. Four out of these tested positive for Enterococcus faecalis – a strain of bacteria known to cause meningitis and septicaemia.

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The university tested a four months out of date foundation, a still in date lip gloss, a nine months out of date blusher, a ten months out of date lipstick, and a four months out of date mascara.

As well as Enterococcus faecalis, the products tested positive for Staphyloccocus epidermis – known to be resistant to antibiotics; Eubacterium – which can cause bacterial vaginosis; Aeromonas – known to cause gastroenteritis and wound infections, and Propionibacterium avidum, a key suspect in the development of acne. Enterococcus faecalis is the potentially deadly strain of bacteria which causes meningitis and septicaema and is one of the biggest killers for newborn babies.”

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According to Dr Low Chai Ling, founder of SW1 Clinic “Most women are totally unaware that their cosmetics are a potential breeding ground for bacteria. But if you think about it you wouldn’t keep food for months after the expiry date, so why would this be acceptable for cosmetics?”

“Pregnant women or mums with small babies need to take extra care especially in light of these findings that showed that the deadly meningitis bacteria was found on several items of out of date make-up,” she adds.

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We get it: once you find that perfect makeup item, whether it’s the perfect shade of red lipstick or the no-flake mascara that makes you look like you’re wearing falsies, it’s tempting to hang on to it until it runs out. After all, replacing old or expired makeup every few months is expensive—so it’s not surprising that one study found that 98 percent of women have used makeup past its expiration date.

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But when you apply old mascara or lipstick, you’re also applying all the bacteria that’s been growing on it while it chills at the bottom of your makeup bag. And no matter what brand you buy or how much you spend on your products, it’s going to happen.

“When you’re constantly dipping into beauty products, you’re introducing bacteria,” comments Dr Low. So every time you apply a product, you’re picking up the bacteria on your face and adding it into the product. That’s definitely reason enough to pay attention to those expiration dates.

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In case you’re not sure how to tell when a beauty product expires, there’s a few things to keep in mind. As a rule of thumb, mascara expires after three months. And when in doubt, products have a little indicator on their packaging that you might’ve missed. It looks like a little jar with a number inside, which denotes the number of months you have after opening it until it goes bad.

Another rule of thumb is not to leave makeup on overnight. Always make sure you give your skin a thorough cleansing as soon as you reach home. “Don’t expect water to do the trick as well” explains Mavis, a makeup artist. “Some makeup are waterproof and needs the proper makeup remover to remove all traces.” Try Undo, a full face makeup remover if you want a quick, one-swipe option for a squeaky clean feel.

For those who don heavy eye makeup and has a penchant for layering on their mascara, try Lemon Quartz facial oil that works wonders to dissolve dirt, grime and stubborn waterproof makeup for a stain-free face.

Lesson learned: it’s important to remember when you bought your makeup so you can keep track of how old it is—because you definitely don’t want to add bacteria to your skin whenever you put on your makeup.

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