Why do you have to wash bed linen after head lice?

Off of a human's head lice cannot not live past 24-48 hours. Therefore, when they have fallen off onto your pillows, blankets, sheets, stuffed animals, etc. they may still be there (alive) after you have treated your hair. So to prevent getting head lice back into your hair, it is best to wash your bedding and dry them thoroughly. Lice and nits will die in temperatures higher than 138 degrees.