My sister has had this twice and it's a symptom of an auto-immune disorder of: "Red ears are also often a classic symptom of relapsing polychondritis (RP), a rare autoimmune disease that attacks various cartilage areas (and sometimes other connective tissue areas) in the body;" My sister has found that a small amount of prednisone keeps this at bay. It's serious because your throat can swell up & cause breathing problems.