Make-up is used by millions of people every day, but they might want to reconsider that after reading a new study.

Researchers from Aston University in Birmingham, UK, have found dangerous microbes such as E.coli and Staphylococci in more than nine out of ten in-use beauty products.

Make-up products are almost never cleaned, and they are often used far beyond their expiration date. In fact, for many of the products, it would be realistically impossible to use them within the expiration date.

A total of 467 make-up products were analyzed. The products were donated by consumers from the UK, following a social media campaign (donors also answered a few questions about make-up habits). This comprised of lipstick (96), eyeliner (92), mascara (93), lip-gloss (107) and beauty blenders (79).

When the team scanned these for pathogens, the results were pretty concerning. The bacteria found in these beauty products range from pathogens that can cause skin infections to some that can cause blood infections, particularly if they are used on sensitive tissue such as eyes or mouth. Given that make-up is sometimes applied over areas with cuts or grazes, the risk of infection with opportunistic bacteria is even higher, particularly in immunocompromised people.

The vast majority of the products were never cleaned — only 6.4% of all collected samples had ever been cleaned. Potentially unsanitary practices were also common: 27.3% of products (largely eyeliner), had been applied in a bathroom, and 28.7% of products had been dropped on the floor.

Beauty blenders, sponges used to apply skin foundation products, were among the biggest culprits. They’ve recently become a sensation in the make-up world, but 35.6% of beauty blenders were used or stored in a bathroom, and 64.4% had been dropped on the floor at least once. As you’d expect from a sponge, the beauty blenders tend to absorb water, dirt, and bacteria, which makes them excellent hosts for all sorts of unwanted bugs.

“Beauty blenders have only been recently introduced as an application product and limited information is available on how best to use or clean them. Our results have shown that these products carried the highest bacterial load during use and more than a quarter were contaminated with Enterobacteriaceae,” the study reads. Several Enterobacteriaceae strains have been shown to be antibiotic-resistant.

Sharing makeup products and makeup testers found on beauty counters may also provide a route for contamination and infection researchers say. Testers are not commonly cleaned regularly, and are often left exposed to the environment and to passing customers.

Although previous research has suggested that make-up products can have disease risk, this is one of the very few studies that analyzes products coming from the real world — and is probably the first one to look at beauty blenders. It’s estimated that 6.5 million such sponges are sold every year, and the figure continues to grow as they are endorsed by celebrities. Since these products are an ideal breeding ground for bacteria, they should be looked at more closely, researchers warn.

The study also highlights that consumers are putting themselves at risk — and they are probably doing so unwittingly (how many consumers out there are aware that beauty blenders are an ideal breeding ground for bacteria?). Producers and regulators should take more action to protect consumers. Cosmetic regulations clearly state that products should not contain pathogenic. organisms, yet 70-90% of all used products were contaminated with bacteria.

Commenting on the new findings, co-author Dr. Amreen Bashir said:

“Consumers’ poor hygiene practices when it comes to using make-up, especially beauty blenders, is very worrying when you consider that we found bacteria such as E.coli – which is linked with faecal contamination – breeding on the products we tested.

“More needs to be done to help educate consumers and the make-up industry as a whole about the need to wash beauty blenders regularly and dry them thoroughly, as well as the risks of using make-up beyond its expiry date.”

There are even more reasons to worry when you consider that make-up products in the European Union are subject to much more scrutiny than those in other parts of the world. EU guidance holds make-up brands to strict hygiene standards of manufacture. People in the US, for instance, are at a much greater risk because the cleanliness of make-up products is less regulated, and there are no requirements to put expiry dates on make-up packaging.

The study has been published in the Journal of Applied Microbiology