Whether you’re locking lips with the love of your life or a total stranger, one kiss can contain as many as one billion bacteria from 278 different species. Fortunately, 95 percent of the bacteria exchanged during a kiss are virtually harmless. But according to a study published in The American Journal of Medicine, there are a number of organisms that can be transmitted through a single seemingly innocuous kiss, and they can cause all sorts of sickening infections and viruses.

Mononucleosis, or “mono,” stands out as one of the most common culprits. With a nickname like “the kissing disease,” it’s no surprise that the condition, often caused by the Epstein-Barr virus, spreads primarily through saliva. But that’s not the only communicable disease you can get from simply kissing someone on the mouth. There are a slew of other slimy bacteria just waiting to hitch a ride on your saliva and travel to a new host to infect.

Click on “View Slideshow” above to find out what could happen the next time you lock lips.