The Scenario: Your best friend just landed her dream job and another just scored a super dope apartment for the low-low. So you plan for a celebratory night out—one that warrants climbing out of your sweats and putting on something that fits like a condom. Now you're all crammed in your bathroom primping, double-sided taping body parts in place, and one of them says, "Let me do your eyeliner." You're a slight germaphobe but at the same time, hey, it's turn up time. You don't sing or dance but you'll be damned if you don't have a Rihanna-like cat eye tonight—so you accept.
The night went impeccably, which means you wake up in a hangover-induced stupor. Also, your left eye, for some reason, is itching uncontrollably. You shuffle to the bathroom while clawing at your eyeballs like a rabid cat. One of said eyeballs of is now a red, watery cesspool. Did you catch something nasty from sharing eyeliner?
The Worst that Could Happen: There are micro-organisms that infect some peoples' eyelashes that can be transferred from person to person by sharing eye makeup, explains Meraf Wolle, professor of ophthalmology at Johns Hopkins School of Medicine. "The organisms can be asymptomatic in some but cause severe symptoms in others," she adds. This explains why your friend, wearing her own eyeliner, woke up just as dehydrated—but her eyes are perfectly fine.
Your bacteria-sharing might have caused conjunctivitis, or pink eye, which is the inflammation or infection of the outer membrane of the eyeball (the white part of the eye) and the inner eyelid. Conjunctivitis can often be caused by bacteria and causes redness, a burning sensation, increased sensitivity to light, and green or white discharge from the eye, says Ralph Paternoster, a New York-based optometrist. Sexy.
Pink eye is contagious as hell, by the way, for the first 24 to 48 hours, my experts tell me. And if the infection is ignored or left untreated, it could lead to blindness.
What Will Probably Happen: Don't panic. The pink eye itself is not very rare if you share eye makeup regularly, but the blindness is. You probably wouldn't leave your puss-ridden eyeball to fester.
Bacteria-related pink eye can easily be treated with antibiotic eye drops or ointments, and the infection should clear up in a week. If you've made the grave mistake of Googling other conditions that could be plaguing your irritated eyes, know that it most likely isn't ocular herpes, which, unlike its more popular sister, genital herpes, is fairly rare. Although it is possible for cold sores from the mouth to shed on to the hands and transmit to eyeliner then potentially infect the eye, Paternoster says, but the herpes virus is very fragile and needs moisture to survive so the odds of that happening are slim.
What You Should Do: Aside from cleaning your eyeliner with rubbing alcohol between uses it's also vital to keeping those corneas bacteria-free. Valery Clermont, is a New York-based makeup artist at a leading cosmetic retailer in New York City and stresses the importance of cleaning eye tools to all of her guests. She ensures she sanitizes all of her tools with rubbing alcohol or alcohol based cleaners in between clients.
"I know several people who have suffered from eye infections because they share makeup products with their friends, or use the same mascara for more than five months," Clermont says. "I often see clients use mascara wands straight from the tester instead of using the clean wands provided, [and do the] same thing with eyeliner and lipsticks."
Wolle cringes at that. "The customer should make sure that some type of alcohol cleaner is used on eyeliner tips and mascara wands," she says.
Although makeup products don't clearly say when their products expire on the packaging, it's recommended to "keep eye makeup for only three to four months to prevent bacterial growth—even if you're the only one using it," Wolle adds.
So the eyeliner-sharing situation would probably be effectively worse if it's old as hell too. Paternoster says, "In reality, sharing eye makeup is akin to sharing a toothbrush; both activities increase the risk of sharing germs that can cause infections."
The next time you and your girlfriends are about to go for a night out, share an Uber or a pizza at 3 am—but use your own damn eyeliner.
Read This Next: What if I Never Change My Disposable Contact Lenses?