I am always finding hidden towels and washcloths that the the "smalls" leave hiding around the house before I can rescue them! I have developed a nose for these crouching towels. Anyway, I learned a few things about towels in general. Depending on the season, once the humidity factor is up I need to wash towel linens more than once a week for the family. The hidden ones aside, even the ones my husband and have hanging in the bathroom simply do not dry out enough to stop eventually smelling. Adding, these slightly damp towels to the hamper also leads to a stinky smell. So, I just decided to wash several times a week. When the kids were born I switched to an eco-friendly laundry detergent that does not leave residue on laundry . I never noticed the residue issue until I started using a natural detergent. But the sticky residue traps odors and dirt. You will notice this stiffness factor if you ever have tried to line dry towels or jeans after using a traditional detergent.
Anyway, the other thing I eliminated from my laundry routine was dryer sheets/fabric softeners. When you have a detergent that is clean rinsing you don't need this. The fibers are naturally freed from the sticky residue and the laundered items are fluffy. While using dryer sheets with yucky chemicals actually coats your laundry with residue that traps dirts and odors. So ditch the fabric softener. You can use wool dryer balls if you feel you need something to further fluff in the dryer. There are times when I still experience a sour, smelly towel and for those times I use a natural towel cleaner called Smelly Towel Cleaner. It's sourced from organic agreements. This is my go-to treatment when I am really serious about needing to get a smell out (like the towel I found hiding in my son's play tent). It just works without worry.
I found mine at http://laundryshoppe.com/. I have not seen it anywhere but online.