Sometimes either we'll accidentally leave a beach towel in the car after swimming or a towel just won't get hung up correctly after a shower. And those towels can really smell bad! Even after washing them with detergent, those towels don't always end up smelling great.
However, by running sour smelling towels through an extra wash cycle with just 1 cup of distilled white vinegar can restore them to smelling nice and fresh.
I have a front-loading washing machine, so I added some towels, added 1 cup of vinegar to the detergent holder, and ran them through a wash cycle with hot water.
When they were finished, they came out smelling much better, and I ran them through 1 more wash cycle with normal detergent and fabric softener.
Now, they're just like new!