The Uhthoff Phenomenom in Multiple Sclerosis

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

Woman drying hair standing at bathroom vanity
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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, even by a small amount, like a half a degree.

This phenomenon 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 a temporary worsening of their vision when exercising.

The 'Why' Behind the Uhthoff Phenomenon

In MS, the myelin (the protective, fatty covering around nerve fibers) is damaged or destroyed by a person's immune system. Myelin is what allows nerves to communicate with each other effectively and quickly. So, when damaged, nerve cells cannot properly transmit messages. Depending on which nerves are affected, these impaired nerve signaling pathways cause a variety of MS symptoms, like blurry vision, numbness and tingling, muscle weakness, and thinking problems.

With the Uhthoff phenomenon, scientists believe that heat acutely worsens these already damaged nerve cells pathways which then triggers current MS symptoms

For example, a woman with MS may notice that her fatigue worsens when her body gets overheated. When her body temperature returns to normal, her fatigue lessens and goes back to baseline.

A key point here is that no permanent neurological damage is done with the Uhthoff phenomenon. In other words, this woman's fatigue (or other MS symptoms that are worsened with heat) are reversible, once her body temperature goes back to normal.

Common Triggers of the Uhthoff Phenomenon

Any source of heat like being in hot and humid weather, using a hair dryer, taking a hot shower or bath, or indulging in a sauna can trigger the Uhthoff phenomenon. In addition, a fever from an infection, exercise, menopause (think of hot flashes), and the peri-menstrual period are other potential triggers.

How to Best Avoid the Uhthoff Phenomenon

Your best bet for preventing the Uhthoff phenomenon from occurring is to identify what your unique triggers are and avoid those. Alternatively, you can partake in cooling strategies that allow you to still enjoy that "trigger" without getting overheated.

Here are some examples of cooling strategies that may be helpful:

  • Drinking cold water throughout the day, especially during the hot summer months
  • Carrying a pocket fan in your purse or backpack in case a situation of being too hot arises
  • Applying a cold washcloth to your wrists or neck when you feel like your body is getting warm
  • Wearing cooling garments like a cooling vest when exercising
  • Wearing a hat and staying in the shade on warm, sunny days
  • Wearing loose, breathable clothing, like cotton

Distinguishing Between a Relapse and the Uhthoff Phenomenon

It can be tricky differentiating between an MS relapse and the Uhthoff phenomenon. In other words, it's normal to wonder if your sudden leg numbness (or other MS symptom) is from the heat or from a new MS lesion in your central nervous system.

One quick way to distinguish between the two is to see if your symptoms reverse when the "heat" trigger is removed, like after cooling down from a hot shower or when your fever returns to normal.

While you may not feel better instantaneously once you are cooled (it can take a few hours, depending on the symptom), your neurological symptoms should return to baseline if heat is the culprit. With an MS relapse, the symptoms will persist.

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.

A Word From Verywell

Managing your MS symptoms is a delicate task and the fact that temperature may affect them as well only complicates this task. Try not to get too bogged down with this extra burden, though.

Do your best to stay cool, and know that if you do develop a worsening of your dreaded MS symptoms, they will be eased soon after the source of heat is removed. Also, be assured you have done no extra harm to your body.

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Article Sources
  • 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.