It can be hard to throw away your favourite beauty buy when it reaches the dreaded 'expiration date,' especially when it's been discontinued or you never got around to using much of it.
If you've ever held onto an old product long after it should have been binned, you're not alone. One US study showed that 98% of women admit to keeping products past their expiration date... and we'd venture a guess that this statistic is rather spot on globally.
After all, how much damage - or rather, bacteria - can an old mascara or lippie really have? Turns out, a lot.
Redditor Semicolon_Expected went viral recently, after they swabbed an old mascara and lipstick to see how much bacteria had gathered over time. Knowing these goods were definitely expired, Semicolon_Expected swabbed them in a petri dish to see what kinds of bacteria might show up.
"So I swabbed my old Revlon Colorstay on a petri dish, the color on one side and the clear on the other side and left it out for 3 days," Semicolon_Expected wrote. "This is what grew after 3 days. I was surprised it grew so much since other cultures I swabbed had more spotty growth and not such big colonies in such a short time with no incubation."
They also posted a photo of some 5-year-old Maybelline mascara, saying, "From the looks of it, there are a lot more colonies but less growth."
The Redditor offered up this explanation:
"Bacteria grows in nutrient rich environments, and agar plates are a nutrient rich environment. Each colony represents at least one bacterium that reproduced to form its own little family, so the plate shows an approximation of bacterial population on the old mascara."
Semicolon_Expected went on to claim that they were looking to refine their process, saying that the flawed petri dish might not be showing the extent of the bacteria. Meaning, they suspect there's much more. Gross, right?
No matter what brand you buy, bacteria will naturally build up over time as the opened product comes into contact with germs.
You should always follow the expiration instructions on the bottle or packaging. As a good rule of thumb, 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. The average life of your foundation and face powders is 12 months. However, most of these products will provide a date on the back of the bottle. A small illustration of a bottle with either 6m, 12m, 24m etc. will appear on the back, indicating how many months it should last once opened.
This article originally appeared on InStyle.