Untoff phenomenon is

Harrison's principles of internal medicine 17th edition. *U/l visual blurring may occur following a hot shower or with physical exercise. Uhthoff's phenomenon (also known as Uhthoff's syndrome, Uhthoff's sign, and Uhthoff's symptom) is the worsening of neurologic symptoms in multiple sclerosis (MS) and other neurological, demyelinating conditions when the body gets overheated from hot weather, exercise, fever, or saunas and hot tubs. Ref Harrison20th edition pg 2345