The redness of the cat's outer auricle may be caused by the cat's frequent ear scratching, fungal infection, bacterial infection, parasitic infection, or inflammation. You need to wear an Elizabethan ring on the cat to prevent the cat from scratching its ears again, and then check the inside of the cat's ears. Whether there are ear mites, parasites or skin diseases on the body, if so, they should be treated in time; if there are no skin diseases or ear mites, and there are no signs of improvement, it is best to take the cat to the pet hospital for examination.