Health knowledge and news provided by doctors.

Uhthoff's Phenomenon in Multiple Sclerosis

Uhthoff's phenomenon and multiple sclerosis

One of the first signs of multiple sclerosis is Uhthoff’s phenomenon, episodes of blurry or dimmed vision associated with a rise in body temperature. Why does this happen and what can you do about it?


Sensitivity to heat affects up to 80 percent of people who have multiple sclerosis. While increases in core body temperature can result in a worsening of a variety of symptoms related to MS, blurry vision is the most common one.

Years ago, before doctors used magnetic resonance imaging and other tests to help diagnose multiple sclerosis, individuals would sometimes be placed in a hot bath. If they experienced blurriness and/or worsening of neurological symptoms such as weakness, they were suspected of having MS.

Temperature changes in individuals with multiple sclerosis impact the demyelinated fibers—including those in the optic nerve. When that happens, the signals that travel from the eye to the brain are compromised and vision is affected.

What can trigger Uhthoff’s phenomenon
Situations that can cause an increase in body core temperature and result in Uhthoff’s phenomenon include exercise, hot baths or showers, saunas and hot tubs, being overdressed, fatigue, fever, sunbathing, and intense emotions. Sometimes the onset of Uhthoff’s phenomenon can be sudden, severe, and even dangerous, especially if accompanied by weakness.

For example, you could be driving a car in hot weather and become overheated if the air conditioning does not work properly. A sudden significant decline in vision could result in an accident.

You might be exercising on a treadmill or bicycle and your vision rapidly fades, causing you to stumble or fall. If you are taking a hot bath or shower, you could lose your balance and injure yourself.

Follow eMaxHealth on YouTube, Twitter and Facebook.
Please, click to subscribe to our Youtube Channel to be notified about upcoming health and food tips.

The good news
The good news is that clear vision returns once the body is cooled and rested, and there usually are no long-term consequences. In addition, episodes of Uhthoff’s phenomenon are not indications that the disease is progressing more quickly or that you have new lesions.

The take-home message is this: Be aware that blurry vision can occur under certain circumstances and that you can avoid and resolve it. Be sure to check out these tips on how to cool down your body temperature--there may be more than you think!

Recent study of Uhthoff’s phenomenon
New findings concerning Uhthoff’s phenomenon were recently reported in the journal European Neurology (2014). A team of researchers wanted to know if patients with multiple sclerosis (54 individuals) and neuromyelitis optica (37) experienced worse neurological symptoms after an increase in body temperature. Neuromyelitis optica is an inflammatory disease characterized by damage to the myelin of the optic nerve and spinal cord.

Among the participants, 48.1 percent (26) of those with MS and 54.1 percent (20) of those with neuromyelitis optica experienced Uhthoff’s phenomenon. The patients reported that sensory and motor symptoms were more frequent than visual problems in both diseases.

When you become overheated, do you tend to experience Uhthoff’s phenomenon, or are other symptoms more bothersome?

Also read about Optic neuritis and multiple sclerosis
Alternative treatments for multiple sclerosis

Flensner G et al. Sensitivity to heat in MS patients: a factor strongly influencing symptomology—an explorative survey. BMC Neurology 2011; 11:27
Park K et al. Uhthoff’s phenomenon in multiple sclerosis and neuromyelitis optica. European Neurology 204; 72(2-3): 153-56