Hard bulging bumps under the skin of dogs may be caused by skin diseases, or connective tissue hyperplasia or small tumors. It is best to go to the hospital for examination to avoid aggravation of the condition. At ordinary times, you should pay attention to keeping your dog clean and hygienic, bathe and deworm your dog regularly to avoid the breeding of bacteria and parasites; if the bag becomes larger and larger, it is best to send it to the hospital for examination. If it is a tumor, you need to ask the doctor whether it needs to be removed.