There are many reasons for irregular menstruation in the twenties, clinically, the twenties are women in their reproductive years, and women in their reproductive years have the following reasons for irregular menstruation: First, the ovaries, such as polycystic ovary syndrome, ovarian dysfunction, can cause irregular menstruation. Second, women in their reproductive years can also suffer from ovarian dysfunction due to contraceptive pills or hormones, resulting in irregular menstruation. Third, women in their childbearing years can suffer from ovarian dysfunction due to stress, fatigue or medication, which can cause irregular menstruation. If women in their reproductive years experience irregular menstruation, it is recommended to go to the hospital for relevant examinations and active treatment.