Cat nail infection, blackening and necrosis is caused by fungal infection, which can be treated with antifungal drugs. If the situation is serious, it is best to take it to the hospital for examination. Nails are easy to be ignored. Usually when a cat digs litter, dirt sticks to the nails. If it is not cleaned up in time, it will lead to infection over a long period of time. Therefore, pay attention to the hygiene of the cat's claws and clean the litter box in time. , disinfect the cat litter box regularly.