One of the tenets of good dental health is obvious—Brush your teeth after every meal. This can help keep your mouth healthy throughout a long life.

Another rule should be just as carefully observed: Do NOT use someone else’s toothbrush. Sharing toothbrushes can shorten your life.

Be safe, not sorry.

But what about emergencies, when you have no other option than to borrow someone’s toothbrush—just once? That’s when this rule is most important. It’s far better to risk tooth decay by not brushing than to risk Hepatitis C or other contagious diseases by sharing—even with those you love.

In fact, anything involving contact with saliva—a kiss, sharing of table utensils, or tasting someone else’s food—can transmit decay-causing bacteria. So, while it’s not likely that avoiding kissing will ever become a trend, you should take care to avoid some of these other high-risk activities.