Brown discharge once you have sex at night may be due to cervicitis and cervical lesions, vaginitis, pelvic inflammatory disease and other diseases. It is recommended to consult a doctor in time to find out the cause and treat it under the doctor’s guidance. 1. Cervicitis and cervical lesions: usually there will be yellow discharge, inflammation or lesions of the cervical mucosa blood vessels are easily ruptured, manifested in the appearance of brown discharge after sex. It is recommended that routine examination of cervical secretions and cervical cancer screening be conducted in a timely manner. 2. Vaginitis: such as mycosis vaginalis or trichomonas vaginalis, may lead to vaginal mucosal congestion, resulting in brown discharge after contact. 3. Pelvic inflammatory disease: mainly inflammation of the endometrium, the endometrial blood vessels are congested, which may lead to rupture of the blood vessels after coitus, resulting in brown discharge. If there is brown discharge, you should seek medical advice to find out the cause, and actively treat it under the guidance of the doctor.