Men should generally replace their underwear every 12 months to avoid potential health issues such as infections or rashes. 

It is possible for bacteria to remain in underwear even after washing. While washing can remove some bacteria, it may not eliminate all of them. It is important to follow proper washing and drying techniques to minimize the presence of bacteria in underwear.

It is not advisable to wear the same underwear for more than 2 years. Over time, underwear can accumulate bacteria, sweat, and other contaminants that may lead to hygiene and health issues. It is recommended to regularly replace underwear to maintain proper hygiene and comfort.