Since this thread has morphed into a discussion of dryers and fabric softener, I thought I'd mention that you can use just plain white vinegar instead of softener. And plain white vinegar in the washer will remove the musty odor from towels that were left in the washer too long.
I'm allergic to virtually all fabric softeners except the original scent of Downey, to all fabric softeners that are in detergents, all dryer sheets, and Tide detergent in particular. It's a very uncomfortable feeling to have to scratch yourself all over, all the time, if someone else washes our clothes and doesn't know about my allergies.