We've all been there – you see an eye shadow or blush compact in your makeup bag but you're not quite sure how long you've had it. No harm in using it one more time, right? Not so fast.
It turns out that all it takes are a few cells from an unwashed hand or a blistered lip and a mascara wand or lip gloss could become a haven for contagious bacteria.
Hundreds of people use makeup counter testers every day, but unfortunately not everyone uses the disposable applicators provided. Dirty fingers dipped in makeup can spread everything from herpes to pink eye.
"You can find staphylococcus, you can find micrococcus…and if you're very unlucky…E. coli, which is obviously from fecal matter," Dermatologist Jeanine Downie said.
That same bacteria might be hiding in your own makeup stash, especially in older products. Antibacterial agents start to break down after about six months.
Former makeup artist Syama Meagher said she still uses products that are months, years and even decades old, like her favorite high school eye shadow from the early '90s.
"If I put it on my finger or my hand and it looks okay I figure, why can't I use it?" Meagher said.
"GMA" wanted to find out just how unhealthy it is to use makeup past its prime, so we collected a few samples to send to a lab: lip gloss from Meagher, liquid eyeliner from our own Juju Chang and mascara and eyeliner pencil from some "GMA" staffers.
ABC News correspondent Andrea Canning had face powder, which was at least a year old, months-old mascara, concealer and worn down lipstick and sent them off to be tested.
Andrea said "it might not be pretty" and she was right -- the results were shocking. Of the 25 samples tested, 11 came back positive for different types of bacteria such as staphylococcus, commonly found on the skin but still potentially harmful.
"This is a bacterium that can cause pink eye…and also skin lesions and rashes," microbiologist Connie Morbach said.
We discovered streptococcus, which is usually found in saliva or mucous, and Morbach said is a bacterium that can cause strep throat.
The other bacteria we detected, micrococcus and bacillus, come from household dust and dirty surfaces. But the worst bacteria we found are called gram negative rods.
"These are organisms that originate in our intestinal system, but also can be found in decayed food," Morbach said.
The amount of bacteria discovered in just one tiny swab was also startling.
"They are actually 100 times more concentrated than what you visually can see on the plate," Morbach said.
The bacteria can not only make you sick, it can also wreak havoc on your skin.
"When you're using contaminated makeup…you can get mild breakouts, all the way to boils and even abscesses on your face," Downie said.
When these women found out exactly what was in their makeup their reactions varied from "gross" to "scary" -- but all of them agreed they should either clean the makeup or throw them out.
Tips to Help Keep Your Makeup Clean:
Sharpen your eye and lip pencils to remove the bacteria on the outer layers. Also use diluted bleach and makeup remover to clean your sharpener.
Wipe down your lipstick, or shave off the top of it with a blade especially if you have shared it with someone else.
Keep the lids and caps tightly closed. If you lost them, throw it out.