Elizabeth Scott, co-director of the Simmons College center for hygiene and health in Boston, says bacteria thrive in the damp, densely woven material, which has lots of nooks and crannies for them to hide in, Men's Health magazine reported.
As people reuse towels, these bacteria can transfer back to the person and cause skin infections, Scott said.
"If you have any kind of wound, you may be infecting yourself with whatever is on the towel," Scott said in a statement.
Scott suggests washing a bath towel at least weekly if only one person is using it, and using fresh towels daily if people share towels.
However, anything that gets soaked -- washcloth, hand towel, or bath towel -- should be washed after every use, Scott recommended.
Don't forget about guest towels; wash them every time there are visitors, Scott advised.