Heat intolerance is a common and often debilitating symptom for many people with MS, affecting 60 – 80% of those diagnosed. As temperatures rise, those affected may experience a temporary worsening of symptoms, significantly impacting their daily activities and overall quality of life. This exacerbation can be triggered by various factors, including warm weather, hot showers, fevers, exercise, or even consuming a heavy meal. To better understand heat intolerance in MS, iConquerMS collects detailed, ongoing data from its members, revealing critical insights into how this symptom varies and evolves over time.
The correlation between heat and the worsening of MS symptoms is known as Uhtoff’s Phenomenon, named after German ophthalmologist Wilhelm Uhthoff. In 1890, he first noticed that people suffering with optic neuritis would get worse when they exercised. It was later determined that exercise was not the cause, rather that it was the resulting heat and rise in body temperature.
Heat intolerance occurs due to demyelination of nerve cells in the brain and spinal cord, which slows down the conduction of signals and exposure to heat slows this process even further. As a result, the body struggles to adapt appropriately to temperature changes. Lesions in the hypothalamus (the part of the brain that regulates the body’s temperature) also inhibit sweating or shivering responses, preventing the body from comfortably adjusting when the mercury rises or falls.
While Uhtoff’s Phenomenon originally focused on visual symptoms, research has since shown that heat can also worsen other MS symptoms. Sometimes, new and unfamiliar symptoms can appear. Fortunately, these effects are usually temporary. Heat does not cause more damage to the nerves, and symptoms improve once the person has cooled down. Just as everyone’s MS experience is unique, heat tolerance can differ from person to person. The type and severity of symptoms can vary widely, as can the recovery time needed after cooling down. Some people may notice their symptoms worsen at lower temperatures, or with less physical activity.
Heat intolerance can be very limiting for people with MS and have a profound effect on their quality of life. There is currently no drug treatment available, however there are a number of simple ways to cool down.
Tips to keep the body cool:
Plan your day. Schedule activities at times when the sun is not at its peak.
Block the sun. Keep an umbrella handy for shade, if needed.
Dress for the heat. Wear lightweight, loose, breathable clothing.
Stay hydrated. Research shows drinking cold water helps people with MS exercise more.
Keep cool drinks available. Store water bottles or pitchers in the fridge.
Explore frozen alternatives. Eating ice chips and popsicles can help.
Try meal prep. The kitchen can heat up quickly, so plan ahead as much as possible.
Eat light. Instead of heavy meals, opt for salads, no-bake dishes and fresh fruit.
Use a spray bottle. Try spritzing with water when the temperature rises.
Wet a washcloth. Hold it to your face or drape it along the back of your neck.
A number of cooling products are available that provide relief from the heat. The Multiple Sclerosis Association of America’s Cooling Distribution Program and the Multiple Sclerosis Foundation’s Cooling Program offer a variety of them at no cost to people with MS that qualify.
Tips to keep the environment cool:
Adjust the thermostat to maximize comfort.
Stay in air conditioning during periods of extreme heat and humidity.
Find a fan. Traditional fans work by evaporating sweat. Misting fans add moisture for extra cooling.
Close curtains or blinds to help keep rooms cool.
Light with LEDs. They put out a fraction of the heat, last longer and use less energy.
Pull the plug. Gadgets and devices create heat, even when not in use. Unplug them before going to bed.
Exercise helps to improve balance, strength, mood, and overall health for everyone. However, as mentioned above, it can also raise core temperature and briefly worsen symptoms for people with MS.
Ways to exercise safely:
Pick a good location. Exercise in an unheated pool or in a cool environment.
Select your timing. If exercising outside, pick cooler times of the day, usually early morning or evening.
Choose the right clothing. Don’t wear too many layers, even if it’s cold.
Be sure to cool down. Take a cool bath or shower after exercising or exposure to a hot environment.
There are plenty of ways to keep cool, which may help people with MS manage some of their symptoms. When using any strategy to cool down, however, moderation is key. Although heat sensitivity is most common, about 20% of people with MS experience worsening symptoms due to cold temperatures (especially spasticity). It is essential that individuals sensitive to changes in temperature work with their healthcare team to develop best practices to control their body temperature and to try to avoid either extreme.
