Cavities Are Contagious? (Yup)
When you think of cavities, you likely think of sugary foods and not keeping up with oral hygiene. The last thing you probably consider is the idea that they could be contagious. When we think of things that are typically contagious, like the flu, for instance, we associate certain behaviors, such as kissing, with increasing the likelihood that we could be "infected." Kissing is one of those behaviors that come to mind. Weirdly enough, a kiss is enough to "pass along a cavity" as well.
This may sound odd but it is true. During a kiss, bacteria can pass from one person to another. Cavity-causing bacteria can also be passed between people. Grossly, leftover food particles can remain in the mouth and like any other bacteria, can go from one mouth to another.
While the saliva present in our mouths aid the balance of good bacteria versus bad bacteria, a high sugar diet can throw this off, altering the pH of the mouth itself, allowing nasty bacteria to thrive and cause cavities. If you exchange kisses with a person who has a mouth filled with a lot of bad bacteria, that can transfer to your mouth and actually cause cavities, even if you have never had one in your life.
If you aren't sure about your kissing partner's oral health, it's probably best to use a mouth rinse after kissing. You should also encourage your partner to keep up with oral hygiene and, of course, keep yours healthy as well. The healthier you keep your mouth, the less likely it is going to be that the harmful bacteria passed between kisses could cause a potential cavity.
So, in short, cavities are actually contagious, as strange as that sounds. It is important to maintain proper oral health and talk to your kissing partner about it too. Nobody wants to deal with cavities!