MS and heat sensitivity

Many people with multiple sclerosis (MS) experience a worsening of their symptoms when their temperature increases. 

Heat intolerance, also called “anhidrosis”, is particularly noticeable when: 

• The weather is hot or humid

• You go in the sun 

• Exercising 

• You have a fever

• You take a hot shower or bath 

(The "hot bath" test used to be used to diagnose MS: the person would be examined while bathing to see if their symptoms increased.) 

At higher temperatures, nerves are generally less able to conduct electrical impulses and nerve transmission slows down. For people with MS, whose nerves are already compromised, even a very small increase in body temperature – as little as a quarter of a degree – can cause their symptoms to flare up. 

Some people notice that their sight gets blurry when they overheat (called “Uhthoff’s symptom”). Other heat-related symptoms include fatigue, tremor, and memory and other cognitive problems. These symptoms are generally temporary, and vanish when the body cools down again: heat itself doesn’t cause any actual further damage to the nerves. 

In some people, certain symptoms (such as spasticity) can actually get worse in cold weather. Generally, sensitive people with MS should avoid extremes of temperature, hot or cold. 

To combat the heat:

• Stay in air-conditioned rooms if the heat and humidity is very high. If that isn’t possible, then oscillating fans can keep the heat down.

• Wear lightweight, loose clothing made out of materials that “breathe”.

• Use cooling products such as mist sprays or cooling gel, especially during exercise. Garments (like vests) are available that contain special crystals that, when soaked in cold water, stay cold for a long time. 

• Iced drinks, ice cubes or ice lollies can keep you cool.

• Exercise in a cool pool, and have cold baths or showers – avoid hot water. 

• Avoid visiting or living in regions with very warm climates – and make sure you find out about the weather before making travel plans.