The redness, swelling and pain on one side of the vulva may be caused by the following reasons: 1. Acute inflammation caused by pathogenic bacterial infection on the affected side can lead to redness, swelling, heat and pain, and it is recommended to keep the vulva clean and, if necessary, to take oral broad-spectrum antibiotics for treatment and to apply Bactrim locally for local treatment. 2. It may be caused by combined infection of the vestibular gland cysts. The clinical symptoms, when there is no co-infection of the vestibular gland cyst, often will not be found, there is no corresponding clinical symptoms, only inadvertently found local small cysts, if the co-infection will appear more serious local pain. It is recommended that intravenous medication be used first to reduce inflammation, and if necessary, an incision is needed to give drainage surgery.