Light red blood after coitus is usually caused by trauma, cervicitis or cervical lesions, physiological factors and so on. 1. trauma: the boys’ action is too rough during the coitus, causing damage to the vaginal mucosa and causing bleeding after coitus. 2. Cervicitis or cervical lesions: patients with cervicitis or cervical lesions, the inflammation or lesions can be stimulated during coitus, resulting in bleeding after coitus, often accompanied by an increase in secretions. 3. Physiological factors: one or two days before the onset of menstruation or within three days after the end of menstruation, the endometrium can be stimulated during sex, resulting in irregular stripping of the endometrium, causing bleeding after intercourse. There may also be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.