Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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 when the body gets overheated from hot weather, exercise, fever, or saunas and hot tubs. First described by Wilhelm Uhthoff in 1890 as a temporary worsening of vision with exercise in patients with optic neuritis, later work revealed the link between exercise and increased heat production. The phenomenon can occur with any neurologic deficit caused by demyelination and is possibly due to the effect of increased temperature on nerve conduction. Many patients with MS experience increased fatigue and other symptoms related to MS when exposed to heat. As a result, many patients with MS avoid saunas, warm baths, and other sources of heat or wear ice- or evaporative-cooling apparel like vests, neck wraps, arm/wrist bands, and hats.