Well, here is my $.02 on this. I was brought up on the "clean towel for every bath" rule and facecloths as well as kitchen towels were changed daily. Sometime in my '30's, my now ex convinced me that there was no reason to use a fresh towel every time, just hang it in the bathroom and change at the end of the week. Great idea. Then a few months later, I noticed that my arms and legs were sporting small perfectly round lighter pigmented spots, Even in summer, they didn't tan and with my normal Mediterranean coloring, made for quite a spectacle. Fortunately they were not on my trunk or my face.
Fast forward to the dermatologist whose first question was whether I used a clean towel for every shower. the culprit turned out to be that the towel stayed damp just long enough for the natural fungi we all have on our skin to multiply rapidly on the towel and hence the result. It took several months of using a nasty smelling antifungal body wash and lotion, but all was eventually back to normal. Let me also point out this had nothing to do with how I wash my toweks (hot water always). Finally, this was before I had central air, so the bathroom stayed somewhat warm and moist for a while. Still, not an experiment I am willing to try again any time soon. Not everyone will have that problem, but since I did... well, you get the idea.