Of course, not everyone is even washing them regularly. The study found 18% of men and 10.5% of women wear underwear multiple times without washing them. According to a new study, you should throw away your underwear every YEAR . . . or it becomes a health risk. When do you throw out a pair of underwear? If your answer is, “Only when it has too many holes for me to count” or “Wait, people throw away underwear?” . . . then listen up. Even though you’re washing them after you wear them . . . hopefully . . . old underwear can still develop a buildup of bacteria like E. coli. That can lead to you getting infections down there. And NO ONE wants those infections. And one more thing: The researchers also say you probably shouldn’t wear underwear when you SLEEP . . . nude is better.