A black tail in a cat is folliculitis, which is usually caused by improper diet or excessive endocrine. The cat needs to be treated in time to avoid aggravation of the condition. First, shave the hair of the affected area, and then clean the black secretions. If it is serious, you can take a medicated bath directly. At the same time, you need to improve the cat’s diet and feed it some lighter food. If it is caused by strong endocrine in male cats, it is best to Get sterilized.