The symmetrical hair loss on both sides of the dog's buttocks may be caused by skin diseases or a diet that is too salty and oily. You need to improve your diet and pay attention to cleanliness. Try to have a light diet, and do not feed your dog greasy or salty food; bathe and deworm your dog regularly, and be sure to dry the hair after bathing to avoid infection with bacteria and fungi, and keep the environment clean and hygienic. You can also spray skin disease treatments on the areas where the dog’s butt is losing hair.