You expect your towel to look nice, feel great, and smell great when you use it. You may, however, discover that your towels occasionally have a smell that is less than desirable.
As a result of being hanging up or jammed in a laundry hamper while still wet or damp, the funky scent may appear when the towels are unable to dry correctly.
Using towels that have become musty is a bad idea, so if you discover this has happened, act quickly.
To begin, you can try washing them in a (fresh, mildew-free) washing machine with hotter than usual water.
If that doesn't work, or if you just want to be extra sure that any lingering odor is gone, you can use a cup of vinegar in the washing machine with your towels.
You may smell the vinegar afterwards. So, wash and dry the towels again normally. A scented fabric softener helps eradicate odors and freshen towels.
According to Modern Bathroom, you may get away with washing them after three or four uses. That is, if you allow them to dry completely between applications.