Sharing is caring — until you get pink eye, herpes, athlete’s foot or a staph infection. These are all things you can pick up from using someone else’s cosmetics or personal care items.

“People can be ‘carriers’ of bacteria and viruses without being sick themselves,” explains dermatologist Elizabeth Tanzi, MD, co-director of the Washington Institute of Dermatologic Laser Surgery in Washington, DC. “Even if someone seems perfectly healthy, you still can develop an infection from using her makeup."

Related: Are You Sacrificing Health in the Name of Beauty?

It’s also possible to have a negative reaction to another person’s unique set of germs. “We all have bacteria and fungi living on our skin as part of our normal flora,” says dermatologist Joshua Zeichner, MD, director of cosmetic and clinical research in the department of dermatology at Mount Sinai Hospital in New York City. “But one person’s normal flora is different from another’s. The microorganisms that sit on a friend’s skin without causing problems for her potentially could cause problems for you.”

Some of the scarier things that have been spreading lately from casual skin contact, Zeichner adds, are antibiotic-resistant staph and MERS, a dangerous respiratory virus. “By sharing what’s in your makeup bag or medicine cabinet, you may make yourself vulnerable to illnesses that are tough to treat,” he says.

Here are seven beauty and personal hygiene tools that you should keep to yourself (or never borrow from someone else), and why.

Razors

A shaving nick can deposit enough blood on a razor to spread any number of pathogens, including staph, hepatitis B and even (though rarely) human immunodeficiency virus, or HIV, says Zeichner.

It’s also possible to develop a bacterial infection such as folliculitis after using someone else’s razor. If you forgot your own razor, save your skin (and perhaps your overall health) by living with stubble or springing for a disposable razor: It will set you back about a buck.

Related: Oral Exam: How Much Do You Know About Dental Health?

Toothbrushes

It’s possible to catch a miserable cold or flu by using someone else’s toothbrush. That’s bad enough. But a germ-laden toothbrush also can spread bacteria, yeast and the herpes simplex virus — that’s right,  cold sores.

“Herpes simplex likes to live on mucosal surfaces,” says Zeichner, “and merely has to touch you for you to catch it.” Just putting someone else’s brush to your lips could leave you with a cold sore. Better to chew gum or swish-and-spit with water than put your mouth on someone else’s toothbrush.

Nail clippers

Why are nail salons required to disinfect manicure and pedicure tools after each customer? One word: fungus. “Fungal spores can live a long time, even on metal surfaces,” Tanzi explains.

In fact, besides never using another person’s nail tools, you also should be careful with your own. Even if you don’t have a fungal infection — and especially if you do — sterilize your clippers after you use them by wiping them down with rubbing alcohol or bleach. Use a different set of tools for fingernails and toenails, and for extra protection at the salon, bring your own clippers.

Related: The Right Way to Trim Your Toenails

Hair brushes

Borrowing someone’s brush may seem harmless until you get a creepy crawly sensation on your head. “Lice is more common than ever before,” Tanzi warns. These parasitic insects can survive on combs and brushes for a day or two. And nits, the sticky eggs of lice that cling to individual strands of hair, can live up to a week, according to the Centers for Disease Control and Prevention. It’s also possible to develop a skin infection from frantic scratching. 

Rather than use another person’s brush, pull your hair into a ponytail or make peace with the bedhead look.

Related: How to Get Rid of Lice

Lipstick and lip gloss

Your friend’s pretty pink lip color may look gorgeous on your pucker too, but a cold sore? Not so much. Never use someone else’s lipstick, lip balm or lip gloss. Viruses such as those that cause the common cold as well as herpes simplex thrive on these products. This is especially true of gloss in a tube, which is a closed, moist environment that’s especially friendly to viruses.

In a beauty emergency, celebrity makeup artist Tomy Rivero recommends lightly wiping off a thin layer of lipstick with a clean tissue before applying.

Mascara and eyeliner

Hello, pink eye! Both viruses and bacteria that can infect the conjunctiva, the clear membrane that covers the eye, are happy to hang out in tubes of mascara and eyeliner. Even if the whites of a friend’s eyes are as pristine as fresh snow, don’t use her eye makeup.

“Because the skin of the eyelid is thinner and more sensitive than most other parts of the body,” Zeichner says, “germs can easily get through even tiny openings and infect a person’s eye. In other words, it’s possible your fringe won’t benefit from someone else’s mascara.

Anything in a pot

Don’t use anything that someone else has dipped her fingers in. This includes concealers, moisturizers and cream blushes, Rivero says. Fingers are a veritable petri dish of germs, some of which linger even after washing. (That’s why the number one way to avoid catching a cold — or spreading one — is to scrub your hands often and well.)

So you don’t contaminate your own pot-based products with germs, use a plastic scoop or wand to dip into them and wash it after.

Related: Brighten Up! How to Safely Exfoliate Your Skin