A woman has menses because of four causes. These are (1) excessive passion, (2) ailment, (3} age, and (4) food or medicine. The cause depending on the age is the most important one. Menses continue till the woman is fifty years old. They begin around the age of eighteen and last for three days in every month. If the menses reappear within eighteen days, there is no bad effect and no dosha (pollution or ashaucha).