What causes ringworm (cat fungus)?

Cat ringworm is a fungal skin disease caused by fungal infection. Undernourished, frail, or low-immunity cats are relatively more likely to catch it. Infection routes are direct and indirect: direct from contacting an infected animal, indirect from contaminated items like food bowls.

Because it is fungal, use antifungal medication; the treatment period is long, so keep applying medicine throughout.