My Hamster Has a Bald, Red, Crusting Patch Behind Its Ear

Hair loss and redness behind a hamster’s ear, from the picture, is usually skin disease from fungus or mites, possibly with bacterial infection, needing microscope confirmation.

If a vet is unavailable, shave the area, disinfect with iodophor or hydrogen peroxide, clear the crust, then apply an antibacterial spray or compound ketoconazole ointment twice daily, with a properly sized collar to prevent licking. Add a nutritional liquid or vitamin B for immunity and keep the cage clean; if no improvement, get a skin exam at a vet.