My cat has two bare patches on its tail that are also dark
Expert Answer
Hello. By observing the photo you uploaded, we can preliminarily judge that the cat has a ringworm infection and that its hair follicles are already damaged. In this case, medicated bath therapy is recommended — you need to shave the cat’s fur first and then give it a medicated bath.
In addition, because the cat’s hair follicles are damaged, you also need to use some medications that repair the hair follicles. This condition usually takes about half a month to show clear improvement, during which the owner should pay attention to careful skin care for the cat.
My cat got bare dark patches on her tail and the article's right, that's ringworm with damaged follicles, so the vet had me shave and medicate-bath her, plus follicle-repair meds. Mine took about two weeks to show real improvement. If your cat's tail is losing fur with dark skin, don't just watch, get a fungal check, because ringworm spreads and the follicles need help to recover, so commit to the baths and skin care, and keep other pets away until it clears.