Blackheads on your dog’s belly may be melanin deposits, fleas, or fungal infection. If your dog’s belly has itching, redness, swelling, dandruff, etc., it is a skin disease caused by parasites or fungal infection, and you need help. The dog is dewormed externally, and then a drug to treat the fungus is applied to the affected area; if there are no abnormalities, then it is melanin deposition, which will not have an impact on the dog's health.