Heat, in whatever form, can affect people with multiple sclerosis and cause MS symptoms to worsen. This can happen if the weather turns hot or humid, when a person is exercising, sunbathing, taking a hot shower or bath, or running a fever — all associated with a rise in body temperature.

Common effects of heat sensitivity include increased fatigue, blurred vision (also called Uhtoff’s phenomenon), loss of balance, or a decrease in concentration or memory.

What causes heat intolerance?

Doctors believe that an increase in body temperature causes nerves to conduct electric signals less efficiently, especially if the fibers (or, myelin, their outer layer) are already damaged by the disease. Damaged nerve fibers already transmit messages to and from the brain (via electric impulses) at a slower pace, and heat furthers slows, distorts, or can stop such communication between the brain and the spinal cord. (The problem can also be caused by a lesion or lesions on the brain area that regulates body temperature, or the area that controls response to an increase in temperature, like sweating.)

In any case, the poor communication worsens MS symptoms until the fibers cool back down again.

Usually, the worsening symptoms caused by heat are temporary, and no further damage to nerve fibers (demyelination) is taking place. Symptoms will ease once the person cools back down.

Heat management

To keep comfortable and cool, people with MS are advised to avoid overly hot or humid environments and direct sunlight, and if they can’t, to make good use of air-conditioning or fans. Also remember to drink cold liquids, suck on ice cubes, take cool baths or showers, avoid outdoor exercise on very hot days, or exercise in non-heated pools or use cooling products like a cooling vest or neck wrap during exercise, and wear lightweight and loose clothing.

Note: Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.