Menstruation is a normal physiological phenomenon, the menstrual cycle is 28 days, can be early or postponed by 1 week, not more than 1 week, if the menstruation 35 days still does not come, belongs to the late menstruation, more than six months does not come belongs to amenorrhea. Adolescent girls usually have their periods at the age of 13-15 years old, if they do not have their periods at the age of 15 years old, it should be taken seriously clinically and needs to be ruled out if it is primary amenorrhea. For women of childbearing age, if they do not have a period for 35 days, the first thing to rule out is pregnancy. Post-menopausal women who do not have a period for 1 year are considered menopausal and can be treated without treatment. Women who are breastfeeding may also not have a period, which is a physiological phenomenon. In short, if your period does not come for more than 35 days, women of childbearing age should go to the hospital to first rule out pregnancy. For women before puberty, during pregnancy, during lactation and after menopause, menstruation is a physiological phenomenon no matter how long it is delayed and can be left alone.