The main reason is that during the menstrual period the body’s resistance is relatively low, low immunity leads to viral infections, so it can cause blisters at the corners of the mouth, the vast majority of which are caused by herpes virus infection, active treatment can be. Although menstruation is a normal physiological period for women, the level of hormones in the body during menstruation will change significantly, leading to a decrease in resistance, so it is easy to cause related diseases. During the menstrual period, it is necessary to strengthen nutrition, pay attention to rest and not to be too tired, so as not to cause a lower resistance to cause the corresponding diseases. In addition, if the corners of the mouth blisters during menstruation, it is best to go to the dermatology department for appropriate examination and treatment, most of the medication will soon be improved.