A hard bag growing on the left side between the anus and vaginal opening may be caused by folliculitis, vestibular gland cysts, warts and other causes. 1. Folliculitis: folliculitis is considered to be caused by Staphylococcus aureus infection, and patients will have red pimples, itching, pain and other manifestations. If there is inflammation of the hair follicles on the left side between the anus and the vaginal opening, the patient will have the symptom of a long hard bag. 2. Vestibular cysts: Vestibular cysts are considered to be caused by congenital narrowing of the gland ducts and vestibular adenitis. Patients will have symptoms such as vestibular gland cysts, localized pain, abnormal vaginal discharge, etc., so patients will have a hard bag on the left side between the anus and vaginal opening. 3. warts: warts may be caused by human papilloma virus infection, the patient will genitals and anus around the skin will appear reddish particles, with the development of the patient will also appear cauliflower, papillary lesions. Therefore, the patient will have the symptom of a hard bag on the left side between the anus and vaginal opening. It is recommended that patients appear between the anus and the vaginal opening on the left side of a hard bag of symptoms, to timely medical treatment, you can take targeted measures under the guidance of the doctor treatment.