My cat has three small bumps on its head; could a neighborhood cat have scratched it, or is it poor deworming? Will the fur grow back?

There are several reasons a cat gets head bumps. A knock or a fight scratch can form a hard scab as blood clots, and bacterial infection makes a pus pocket; check the head, trim hair around the spot, wash with warm water and disinfect with hydrogen peroxide, then apply ointment.

If there is no scab but a round or oval bald patch with gray scales, it is likely ringworm or mites. Have a vet do a skin scrape to confirm, treat the cause, disinfect the environment, and use medicated baths if severe. During treatment use an Elizabethan collar and regular external deworming and mite spray.