In Philip Tierno’s mind, a moist or damp towel is practically a living organism. He says, “a damp towel is growing”. Tierno is a microbiologist at the New York University School of Medicine.
Towels serve as ideal breeding grounds for germs because they contain many of the requirements for microbial life: water, warm temperatures, and plenty of oxygen. Where there is moisture, there are microbes.
Due to this factor, Tierno highly recommends only using a bath towel no more than three times before washing it. This suggestion is also under the assumption that it gets completely dry after each use.
One way to tell that a bath towel gets dry after each use is by smell. A towel that has remained damp for too long will have an odor. “If the odor is coming from the towel, wherever there is odor, there are microbes growing, so it should be washed,” Tierno said.
By drying yourself with a towel coated in bacteria, you are likely transferring that bacteria onto your skin, basically undoing the entire purpose of taking a shower in the first place.
Also, if you are sharing a towel with other people, you could come into contact with organisms that your body isn’t used to dealing with. For example, Staphylococcus aureus, Tierno said, “which may give rise to a boil, pimple, or worse, an infection.”
It is important to keep in mind, however, that not all microbes are bad for us. In fact, many of them are relatively harmless. Also, some may even be beneficial to us in the long run. According to an idea called hygiene hypothesis, exposure to germs and certain infections, especially at a young age, may actually help prime the immune system so it can defeat foreign microbes more easily in the future.
But even still, no one likes a smelly towel. Especially when that odor means the cloth is swarming with microbial life.
“The idea is to be prudent and to be aware,” Tierno said.