MS, Hot Weather and Tips to Stay Cool

Why people with multiple sclerosis need to keep cool.

Medically reviewed in December 2021

For most people with multiple sclerosis (MS), summer is no picnic. Heat waves and high humidity levels often mean worse MS symptoms, like visual disturbances, weakness and fatigue. It's thought that nerve cells damaged by the condition have even more trouble operating in higher temperatures.

Nerve cells in the brain are no exception. Researchers are now seeing how a hot, sunny day leads to cloudy thinking in people with MS—and what the brain does about it.

When the brain heats up
An October 2013 study of 28 people, published by Brain Imaging and Behavior, found that participants had worse MS symptoms on warmer days. Using MRI scans, the researchers looked at how rising outdoor temperatures affected the brain. In the 26 women and two men, simple tasks increased activation in powerhouse areas of the brain—areas normally reserved for more complex tasks, like planning and multitasking. However, the same wasn't true in people who didn't have MS.

While that may sound like the brain is performing like an all-star despite the heat, researchers believe it's a coping mechanism. The brain is getting the simple task done, but it's requiring more energy to do so.

What happens, and why?
MS, at its heart, is a nerve and nervous system problem. The condition damages the protective sheath that encases your nerve cells, and that damage slows down nerve signals. This leads to symptoms such as:

  • Vision problems
  • Balance and coordination trouble
  • Tingling or numbness
  • Muscle weakness
  • Concentration and memory issues

Researchers believe that the heat further slows down nerve signals, causing more or stronger symptoms. It’s not just the weather that can increase symptoms, either—sunbathing, hot tubs, exercise and even a fever can all make MS symptoms worse. These heat-induced symptoms are thought to be temporary and cause no long-term damage, however.

How to keep your cool
Before the next heat wave, consider these smart tips:

  • Avoid the heat. Prevention is best, so limit outdoor activities when it's really hot or humid. Get your fresh air during cooler parts of the day, like early morning or evening. A morning walk can even help you sleep better.
  • Dress for success. When you're out in the sun, wear a wide-brimmed hat and loose, breathable clothing in light colors. You can also try cooling vests and headbands, or don a refrigerated wet towel or shirt before you head out.
  • Go for a swim. Wading or stretching your arms and legs in a shaded pool can be refreshing and offer other great health benefits. Just be sure the water temperature is under 85 degrees.
  • Keep your cool. When you're indoors, run the AC or fan. Reach for cold drinks or a frozen treat. And when you can't get to the pool, jump in the shower for a cool rinse.

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