You might share everything with your partner, from bites off your dinner plate to your car. But there’s one thing you should hold back on: Your toothbrush.

A USA Today poll revealed that more than a quarter of respondents thought sharing a Wi-Fi password was more personal than sharing a toothbrush. A British Dental Health Foundation survey found an even more disturbing number: Over 60% of participants would let their partners, children, friends and even celebrities borrow their toothbrush.

But there can be such a thing as being too generous.

The human mouth contains plaque, food debris and hundreds of types of bacteria. When a couple shares the same toothbrush, they also share the same bacteria. This can make themselves more susceptible to tooth decay, gum disease and other oral infections if the partner has these oral conditions. The possibility of infection is augmented when someone’s gums bleed: Open wounds in the mouth allow blood-borne illnesses a way into the body.

So as much as you care for your partner, be selfish in love – get your own toothbrush. You can also help prevent oral disease by storing your toothbrushes upright and separated. And who knows, having separate toothbrushes might even improve your relationship.