How long lifetime at most for one towel

Normally only when the towel broke out or becomes hard, can it then be out. But from the scientific angle when shall we change one new towel In daily life? Today our textile expert told us the truth, it should be changed nearly every 30 days for each individual,and at most 40 days. Otherwise, it should be boiled in high temperature. in order to be sterilized and softened.