Because cats have sebaceous glands on their tails, when these glands secrete too much oil, the tail becomes greasy. This can be caused by genetics, hormonal imbalances, or environmental factors (such as diet, grooming habits, ambient humidity, and temperature).
Additionally, certain parasites, such as Demodex mites, can also cause a cat's tail to become oily. These parasites live on the cat's skin, causing skin inflammation and excessive oil production.
