Sudden growth of cysts on the outside of the left vulva may be caused by folliculitis, Bartholin’s gland cysts or vulvar cancer. 1. Folliculitis: If women wear tight underwear, they will keep rubbing the vulva when they are moving around, and excessive friction may damage the skin of the vulva and cause bacterial infection, leading to folliculitis. It can also be accompanied by itching, redness, swelling, pain and other discomfort. 2. Bartholin’s gland cysts: when the Bartholin’s gland is blocked and the secretion cannot be discharged normally, and accumulates in the Bartholin’s gland ducts, cysts may be formed, accompanied by symptoms such as vulvar swelling and discomfort during sexual intercourse, and when there is inflammation, it may also show symptoms such as fever, vulvar burning and pain. 3. Vulvar cancer: mostly seen in postmenopausal women, usually manifested by symptoms such as vulvar lumps, persistent itching of vulva, vaginal bleeding, thickening of vulvar skin. There are more reasons for women to have cysts on the left side of the vulva, so it is recommended to go to the hospital to do relevant examination and be judged by professional doctors to make a clear diagnosis before treatment.