There are several common reasons for brown discharge during menstruation: 1. It may be due to gynecological inflammation, commonly vaginitis, pelvic inflammatory disease, endometritis, salpingitis and so on. When there is inflammation, it can lead to an increase in the permeability of the skin mucous membranes and also of the small arteries or capillaries, because most gynecological infections are caused by bacterial infections. When there is a bacterial infection the bacteria will also have abnormal secretions as well as a buildup of inflammatory cells such as leukocytes, neutrophils, and other immune cells, and the secretion substances formed during different bacterial infections are also different. These combined factors can lead to abnormalities in the first two days of menstruation, namely the formation of brown secretions.2. For women with multiple sexual partners, it is important to suspect the presence of sexually transmitted diseases, such as AIDS, syphilis, warts and so on. When a woman is infected by these STD viruses, it can also cause the body to produce abnormal brown discharge.