Drying towels between uses
Short answer: Spread the towel out fully rather than hanging it folded on a hook. A folded towel never dries completely and starts to smell after two days.
Why folded does not work
A towel on a hook touches itself on both sides of the fold. There is no air in between, and the moisture stays. That is where the bacteria grow and the smell arises.
How to hang it properly
Spread it over a rail so the whole surface is in contact with air. A towel rail gives more room than a hook. See bamboo towels.
How often it needs washing
Every third or fourth use if it dries completely in between. If it does not dry, after every one or two uses. See Turiform and bamboo bedding.
Frequently asked questions
Why do towels smell sour
Because they never dry completely. Air is the answer, not more soap.
Does airing the bathroom help
Yes, a great deal. Open the window or leave the door open after a shower.
Can a smelly towel be saved
Wash at 60 degrees with a cup of vinegar in the softener compartment.