Cats lose their tail hair due to reasons ranging from medical conditions to flea infestation to environmental issues. Unless the cause is obvious, the best way diagnose the problem is by visiting a veterinarian to have the cat examined. According to PetMD, tools to diagnose hair loss include blood tests, X-rays and biopsy of skin scrapings. VetInfo states that ultrasound can also be used as a diagnosis tool.
According to VetInfo, the most common reason for hair loss on the tail is a flea infestation. When fleas bite, it causes irritation. Because the cat has easy access to its tail, it will bite and chew on it to relieve the
irritation, thus causing hair loss, VetInfo explains. The cat may also be allergic to the flea bite; in that case, according to WebMD, itching will be intense, and infection or hot spots may develop.
Other causes of tail hair loss in cats, according to VetInfo, include allergies, stress, skin infections and poor diet. WebMD notes that stud tail can cause tail hair loss; this condition is caused when a smelly, waxy substance oozes out of a gland located near the base of the tail. Other diseases associated with tail hair loss in cats include hyperthyroidism and hypothyroidism.