Every time you touch your makeup, you transfer all the dirt and tiny little organisms on your skin into the product. The same goes for any brush or sponge applicator — all those germs will inevitably get into your makeup, too. 

And it's safe to assume that the average person is not diligently washing and sanitizing their hands and brushes before and between using products. So over time, makeup products will become full of all kinds of things.

"The makeup will contain your natural flora from your face, which is kind of like a germ fingerprint," Susan Whittier, PhD, associate professor of clinical pathology and cell biology at New York-Presbyterian/Columbia University Medical Center, tells BuzzFeed Health.

Germs include bacteria, protozoa, viruses, and fungi, and they exist everywhere. Actually, everyone has a specific bacterial ~flora~ (germ profile) on their skin and inside their bodies, so germs are totally natural. "These include things like Staphylococcus epidermidis, Streptococcus viridans, and Micrococcus," Whittier says. 

But you should avoid pathogens — which are different from normal germs. A pathogen is any bacteria, virus, or other organism that causes disease or infections. Think: staph aureus, E. coli, strep, salmonella, etc. 

For instance, if you apply makeup with dirty hands, use your products when you're sick, share makeup with someone else, never clean it, etc. And it's not just that you’re transmitting germs to your makeup — you’re then getting that bacteria-ridden makeup in your mouth, eyes, and any broken skin.  

"If you have an open cut or pimple, the dirty makeup could get in there and cause an infection like staph — or if it's your eye, it can cause irritation or conjunctivitis [pink eye]," Whittier says. And viruses like the flu or a cold — or even the herpes simplex virus — can also survive on lipsticks for days to weeks thanks to the waxes and proteins in them. 

So no, contaminated makeup won't kill you, but it could cause a nasty skin or eye problem that requires a doctor's visit. Not to mention, there might be poop in your old makeup, too. "After three months, makeup will probably also have some fecal matter since it's usually stored and used in the bathroom next to the toilet," Whittier says. Fantastic. 

"For most products, you can spray them with alcohol or use an alcohol wipe on the outermost layer — when it dries, it'll be clean," Whittier said.  

That sounds easy enough, actually.

All the makeup we tested came from BuzzFeed employees, and each product had these three things in common: 

 1) It was something they used every day as part of their makeup routine 

 2) It was at least three months old 

 3) It had never been sanitized or cleaned before  

That sounds easy enough, actually.

Then we transferred the makeup on the swab to a petri dish filled with nutrient agar, which is food for bacteria and other germs to grow. For the Beautyblender, we cut a small piece and put it in a test tube full of liquid amies, vortexed, then swabbed the solution onto a petri dish. 

We popped the petri dishes into an incubator set to 98.6 degrees (the average internal body temperature of a human) and waited 48 hours.