Many people know that colds, chickenpox, and even yawns are contagious, However did you know that dental cavities can be contagious too?  Sugar-laden candy bars are not the only cause of tooth decay. Tooth decay actually results when bacteria in your mouth feed on food debris and produce acid as a byproduct. This mix of food, acid, saliva, and germs clings to your teeth as a filmy substance called plaque, which can erode teeth enamel and cause cavities to form.  

No matter what you eat, cavities will not form without the help of such bacteria. These germs can spread from mouth to mouth via shared food and utensils, sneezing, kissing, and more, according to Edward “Trey” Wilson, DDS, a dentist in private practice in New York City and New Hope, Pa. — making cavities contagious.