"So how many times can you use your towel before before concentrations of your own flora get so out of hand that you need to wash it? "If you can dry it completely, no more than three times max," Philip Tierno, a microbiologist and pathologist at the New York University School of Medicine, told Tech Insider.
And this is assuming that you're hanging it somewhere dry so that it can completely air out. "A damp towel is growing," Tierno said. "If there is odour coming from the towel, wherever there is odour, there are microbes growing so it should be washed." "The idea is to be prudent and to be aware," Tierno said. Mostly, aware that your towel is disgusting. And you're probably not washing it enough.
www.sciencealert.com/how-often-should-you-wash-your-bath-towel-according-to-science
So I've never been a fan of sticking huge bath towels over every radiator to get them dry fast, which is why I'm happier putting damp towels straight into the laundry. Personal preference. I also love the feel of a clean towel that hasn't gone limp with use.