Science says that your toothbrush is likely covered in dookie dust. Okay, they didn't use the term "dookie dust" but yeah, there's a good chance that you're brushing your chompers with poo particles. GROSS!
Oh, and if you have roommates you're probably brushing your teeth with their doo-doo dander too!
According to a recent study (because this isn't the kind of info you hold off on revealing) there's a 60 percent chance that your toothbrush has old, stanky, microscopic, shit particles all over it. And it jumps to 80 percent if you share the bathroom with another person (100% if that person a frequent Taco Bell patron).
So, assuming that your roommate isn't an evil sociopath that wipes the toilet bowl with your toothbrush every chance they get, how does this incredibly gross occurence happen? Well, an invisible poop demon is crapping on your toothbrush... I kid, I kid.
Fecal coliform bacteria flies out of the toilet bowl every time you flush (or fart) and rinsing it off with hot water doesn't do much. In fact, you're pretty much powerless against fecal coliform's aerial poop attack.
"Using a toothbrush cover doesn't protect a toothbrush from bacterial growth, but actually creates an environment where bacteria are better suited to grow by keeping the bristles moist and not allowing the head of the toothbrush to dry out between uses," said Aber.
So I guess just don't keep your toothbrush in the bathroom or start brushing with bleach -- though your dentist probably wouldn't recommend that.