What is the Uhthoff Phenomenom in Multiple Sclerosis?

How a Rise in Your Body Temperature May Exacerbate Your MS Symptoms

Man overheating while doing dishes
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The Uhthoff phenomenon is a unique sign in multiple sclerosis characterized by a worsening of one or more MS symptoms when the body's core temperature is elevated. It was first described by Wilhelm Uhthoff, a German eye specialist, in the late 19th century. He noticed that people with optic neuritis, a common symptom of multiple sclerosis, had temporary worsening of their vision when exercising

What Causes Uhthoff Phenomenon?

In MS, the myelin — a protective covering around nerve fibers — is damaged or destroyed by a person's immune system.

The myelin is what allows nerves to communicate with each other effectively and quickly. When damaged, nerve cells cannot properly transmit messages. Depending on which ones are affected, these impaired nerve signaling pathways cause a variety of MS symptoms, like blurry vision, numbness and tingling, muscle weakness, and thinking problems.

In the Uhthoff phenomenon, scientists believe that heat worsens these already damaged nerve cells pathways, which exacerbates current MS symptoms. 

For example, a person may notice her fatigue or walking worsens when her body gets overheated. When her body temperature returns to normal, her symptoms go away. No permanent damage was done, meaning the fatigue or problems walking are reversible.

What Triggers the Uhthoff Phenomenon?

Any source of heat like hot and humid weather, using a hair dryer, a hot shower or bath, or a sauna can trigger this phenomenon.

In addition, a fever from an infection, exercise, menopause, and the peri-menstrual period are other potential triggers.

How Can I Avoid the Uhthoff Phenomenon?

There are number of cooling strategies that can help you avoid the Uhthoff phenomenon. These include:

  • drinking cold water throughout the day
  • carrying a pocket fan in your purse or backpack
  • applying a cold washcloth to your wrists or neck
  • wearing cooling garments like a cooling vest
  • wearing a hat and staying in the shade on hot, sunny days
  • wearing loose, breathable clothing, like cotton

How Do I Know if I'm Having a Relapse or Experiencing Uhthoff Phenomenon?

It can be tricky to distinguish between a MS relapse and the Uhthoff phenomenon. One quick way is to see if your symptoms reverse when the trigger is removed, like after cooling down from a hot shower or when your fever returns to normal. It's important to note that you may not feel better right away. It could take a few hours, for instance, for your fatigue to be restored after removing the heat source. 

That being said, it's still a good idea to contact your neurologist or your MS nurse, especially if you are unsure. An MS relapse may require treatment, like steroids, whereas a symptom of Uhthoff phenomenon does not require medication — only removal of the trigger and reassurance. 


Birnbaum, M.D. George. (2013). Multiple Sclerosis: Clinician’s Guide to Diagnosis and Treatment, 2nd Edition. New York, New York. Oxford University Press.

Frohman TC et al. Uhthoff's phenomena in MS--clinical features and pathophysiology. Nat Rev Neurol. 2013 Sep;9(9):535-40.

Multiple Sclerosis Society. (2013). Fact sheet: Hot and cold - the effects of temperature on MS. Retrieved January 7th 2016. 

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