Black spots on the inside of the toenail may be caused by external forces, nail fungus disease, onychomycosis and other factors. It is recommended to pay attention to the care of the affected area, external, internal antifungal drugs, if necessary, through surgery for treatment. 1. The role of external forces: previous impact on the toenail by external forces or shoes too crowded feet, may lead to bruising under the toenail, from the appearance of the toenail may have black spots. It is suggested to observe closely and choose suitable shoes and socks, which may recover by themselves with time. 2. Nail fungus disease: Nail fungus disease is caused by fungi invading the nail plate, resulting in black spots on the toenail. It is recommended to carry out the appropriate examination, and after diagnosis, use topical amorolfine rubbing agent, cyclopentanone nail coating, and if necessary, with oral itraconazole capsules, terbinafine hydrochloride and other medications. 3. Nail nevus: There is another possibility of nail nevus, such as a pigmented nevus at the root of the toenail, which may lead to black spots on the surface of the nail. The pigmented nevus will increase in size or growth, and if necessary, it will be surgically removed and pathologically examined. To summarize, the appearance of black spots on toenails is related to various factors, it is recommended not to deal with it blindly, you can go to the dermatology department of the hospital to understand the cause first, and then give targeted treatment.