My cat has a small patch on top of its head—I don’t know if it bumped it or has a skin disease

If a small patch of skin on a cat’s head is abnormal, it may be a scab from a bump, injury, or a skin disease. Watch the spot closely; if there is clear pain, swelling, red spots, itch, hair loss, or erosion, it is very likely a skin infection—take the cat to a vet for a scraping and diagnosis, then treat by infection type.

If the spot has no much dandruff or inflammation, treat it as a wound for a few days to see if it improves; during treatment put on an Elizabethan collar to stop scratching, disinfect the spot with iodine, and keep it dry.