In most cases, it’s good to share. But here’s a list of things you should never share, according to our friend microbiologist Dr. Charles Gerba:

First: Shopping carts. I don’t mean to gross you out, but a study found dangerous bacteria and viruses on 80 percent of shopping cart seats and handles. Dr. Gerba says that makes sense, because carts come in contact with everything from raw chicken to diapered baby bottoms! That’s why he says you should always disinfect shopping cart handles and seats with a sanitizing wipe, and wash your hands after you shop.

Next, never share: Razors. Dr. Gerba says whether you see them or not, shaving creates tiny nicks and cuts that allows blood to be transferred to razors. So, if you use someone else’s razor, you’re exposing yourself to blood-borne diseases like hepatitis B and C, or even HIV.

For the same reason, don’t share: Toothbrushes – even with someone you’re kissing. Dr. Gerba says brushing scrapes the skin on your gums, exposing you to blood-borne germs. Plus, you’re more likely to transmit cold and flu viruses through a toothbrush than you are through kissing.

One more thing you shouldn’t share: Cell phones. Dr. Gerba says the problem with cell phones is that people always touch them, but rarely clean them.  And since most people don’t wash their hands after using the bathroom, it’s common to find dangerous bacteria all over cell phones! And get this: Research shows that women’s cell phones tend to be germier than men’s, mostly because women get twice as many colds as men.