Can I get cooties from kissing?

Cooties (in this case, oral bacteria) can be passed on from one person to another any time saliva is shared. This transmission of bacteria can occur when kissing. In the dental field, the evidence of these cooties are seen in the form of cavities, also known as dental caries. The bacteria that cause cavities, such as Streptococcus mutans and Streptococcus sobrinus, can introduce cavities into a once cavity-free environment. Yes, cavities are contagious.  This phenomenon can be seen in the transference of these bacteria from mother to child, even if the baby does not yet have teeth!
When these specific bacteria exist in the mouth, they feed on food we leave behind, and create very acidic waste. By nature, anything that feeds, has to create waste. There is no bathroom in our mouths for the bacteria to use for waste disposal. When the bacteria create waste, it changes the environment on the exposed surfaces of our teeth, and this acidic environment breaks down our enamel. Over time, if the bacteria and their waste products are left unchecked, the enamel will develop a soft lesion known as caries.
One way to decrease your risk for cavities is to improve your oral hygiene. Excellent oral hygiene ensures that there are no food particles left for the bacteria to feed on. With no food left in your mouth after eating, the bacteria don't have as much food to use in creating waste, and thus decreasing your chances of getting dental caries. Also, improving your diet by eating more complex carbohydrates will prevent bacteria from easily digesting simple sugars into waste. Another way to prevent these bacteria from populating the mouth, is to be cautious with whom you are sharing your drinks, foods, and kisses!