"Make-up products used every day by millions of people in the UK are contaminated with potentially deadly bugs, such as E.coli and Staphylococci, because most are not being cleaned and are used far beyond their expiry dates," said study lead author Amreen Bashir from Aston University in the US.
According to the study published in the Journal of Applied Microbiology, bacteria that can cause illnesses ranging from skin infections to blood poisoning if used near eyes, mouth or cuts or grazes were found in nine out of ten of the products.
This risk is amplified in immunocompromised people who are more likely to contract infections from opportunistic bacteria.
The relatively new beauty blenders - sponges used to apply skin foundation products - were found to have the highest levels of potentially harmful bacteria - with the vast majority (93 per cent) not having ever been cleaned, despite more than two thirds (64 per cent) being dropped on the floor at some point during use.
The research looked at beauty blender products - hugely popular make-up sponges used to blend foundation and contouring on the face.
Often endorsed by celebrities, these sponges are estimated to have sold over 6.5 million worldwide.
The researchers found these products are particularly susceptible to contamination as they are often left damp after use, which creates an ideal breeding ground for harmful bacteria.
"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," Bashir said.
The findings reveal that consumers are unwittingly putting themselves at risk, and that manufacturers and regulatory bodies should do more to protect their customers by making expiry dates and cleaning requirements more prominent on packaging.
EU guidance holds make-up brands to strict hygiene standards of manufacture and states that E.coli in particular should not be found in any concentration in new cosmetic products.
However, there is currently limited consumer protection around the risks of contaminating products while in use.
According to the study, post-Brexit, UK consumers could be at even greater risk as they will no longer be protected by EU regulations and could find themselves purchasing more beauty products from the US - for example - where there are no regulatory requirements to put expiry dates on make-up packaging at all.
( With inputs from IANS )