Everyone has at least one dirty habit. That's why researchers did a poll recently, asking 1,000 people about their dirtiest habits of all. Here are the results, along with intel on which bad habits may also be bad for your health! These come from the new book Let's Play Doctor, by Mark Leyner and Dr. Billy Goldberg. Dirty habit #1: Wearing dirty clothes. A whopping 85% of people admit they've thrown on barely worn shirts or jeans before, but over 40% admit to wearing dirty underwear! That's bad news, according to microbiologist Dr. Charles Gerba. He says the average pair of day-old underwear contains traces of fecal matter, and about 100 million E. coli bacteria! Since germs spread easily once they're lumped inside a laundry hamper, Dr. Gerba says you should avoid wearing anything that's come in contact with day old underwear. Dirty habit #2 : Not brushing every night. Only 57% of people say they brush and floss their teeth each night before bed! That means the other 43% are setting themselves up for a lifetime of cavities, gum disease and a possible heart-attack! Why? Your mouth naturally develops less bacteria-killing saliva when you sleep. So any germs in your mouth will multiply overnight, increasing your risk for health problems. Know this: The gases emitted from your breath after a night of not brushing are similar to the gases you'll find in most port-a-potties! Here's one more dirty habit that's not as dirty as you think: Not showering every day. 33% of people admit they skip bathing some days, but from a health standpoint, experts say that's really no big deal. Not showering simply allows sweat to build up on your body, and while sweat promotes bacteria build-up, it's not the kind that'll make you sick. It's just the *smelly kind of bacteria that keeps all your friends away.