Swelling in a female dog's private area can be due to several reasons, including vaginitis, which causes vaginal inflammation and swelling. Heat cycle can also cause temporary swelling. Infections such as bacterial infection, urinary tract infection, or canine herpesvirus can lead to swelling and vulvar discharge. Additionally, foreign bodies, vaginal neoplasia, or structural abnormalities could be the underlying causes. Dogs who have not been spayed may develop vaginal hyperplasia, which can also cause swelling. Vaginitis typically affects young female dogs but can also affect female dogs of all ages. A physical examination and bacterial culture are recommended to diagnose the exact cause and determine the appropriate treatment.