Have you ever wondered why the summer heat or even a really hot shower can make your multiple sclerosis (MS) symptoms worse? For many people with MS, even a slight increase in body temperature can cause fatigue, blurred vision, or muscle weakness.
Between 60 and 80 percent of people with MS report heat sensitivity, which is known as Uhthoff phenomenon or Uhthoff syndrome. In fact, heat-induced MS symptoms are so common that in the 1950s, the “hot bath test” (which is exactly what it sounds like) was used as a diagnostic test.
Keep reading to understand the science behind why heat makes your MS symptoms worse, and expert tips on how to stay cool when temperatures start to rise.
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Why MS Symptoms Get Worse When You Get Overheated
While scientists don’t completely understand why heat exacerbates MS, they have identified two key factors that contribute to the Uhthoff phenomenon.
Slower Nerve Signal Transmission MS causes damage to the protective covering of the nerves, called myelin, in your brain, spine and optic nerves. When the body heats up, it further impairs the ability of the damaged nerves to send needed messages to your body to function optimally, says Sarah Anderson, PharmD, the senior director of clinical resources and programming for the National MS Society.
Impaired Temperature Regulation Lesions — areas of damaged myelin — in the brain areas responsible for controlling body temperature may hinder the body's ability to sweat or flush heat effectively.
“Natural compensation mechanisms to regulate the body in extreme environments are not working right in people with MS. People without MS sweat when they get hot and need to cool down, but people with MS may not,” says Dr. Anderson.
Common MS Symptoms That Get Worse in Hot and Humid Weather
“Heat generally only leads to temporary worsening of symptoms — it does not cause more disease activity, such as demyelination or damage to the nerves themselves. The symptoms caused by heat improve after you cool down,” says Anderson.
Neurological symptoms caused by increases in core body temperature can include:
Fatigue
Weakness
Numbness and tingling
Balance issues
Tremor
Cognitive difficulties, such as problems with attention and concentration
Slowed reaction time
Practical Strategies for Managing Heat Sensitivity
If you’re in the majority of people with MS who experience the Uhthoff phenomenon, it doesn’t mean that you can’t be physically active or go outside during the spring and summer. There are simple preventive measures you can take to reduce your chances of overheating.
Stay Cool Indoors
Air-conditioning, when available, is often the best way to stay cool indoors in hot weather, but it can be expensive. A few other strategies can help.
Air-Conditioning Air-conditioning is your best friend during hot weather. It helps maintain a comfortable indoor temperature and reduces humidity, both of which are crucial for managing heat sensitivity.
“If an air conditioner is needed to help minimize symptoms, the cost of the equipment may be tax deductible if your healthcare provider has written a prescription for it,” says Anderson.
Window Coverings Closing your shades or blinds when it’s sunny out helps to block the sun’s heat as well as its light, so your home doesn’t heat up as much.
Fans Fans, especially when combined with moisture, can enhance cooling. Placing a bowl of ice in front of a fan can create a makeshift air conditioner, circulating cooler air throughout the room.
Cool Showers or Baths A cool shower or bath can provide immediate relief by lowering your body temperature. Ensure the water is not too cold to avoid shock to your system.
Cooling Towels and Packs Applying cooling towels or packs to pulse points like the neck, wrists, and forehead can effectively lower body temperature. These products are designed to absorb heat and provide a cooling effect.
Lightweight and Breathable Clothing Wear loose-fitting, lightweight clothing made from natural fibers like cotton. These materials allow your skin to breathe and facilitate heat dissipation.
Stay Cool Outdoors
Time outdoors has physical and mental health benefits, but it’s important to be proactive about staying cool when you go outside in warm weather.
Time Your Activities Engage in outdoor activities during the cooler parts of the day, such as early morning or late evening, to minimize heat exposure.
Seek Shade When possible, stay in shaded areas when outdoors. Use umbrellas or hats to provide additional protection from direct sunlight.
Hydration Drink plenty of cool fluids, especially water and electrolyte drinks, to stay hydrated. Popsicles can also provide cooling relief.
“Proper hydration helps regulate body temperature and prevent overheating. To increase your water intake, drink a glass of water with every meal and carry a water bottle (preferably insulated to keep water chilled) that you can refill throughout the day,” says Anderson.
Cooling Vests and Accessories Use cooling products such as vests, neck wraps, and bandanas during exercise or outdoor activity, says Anderson.
There are different types of cooling clothing. Some are soaked in water and cool your body through natural evaporation. Others are frozen and provide cooling comfort until they “melt.” The most high-tech models circulate cold water via tubing and require an external cooling reservoir.
Check with your insurance company to see if any of these devices are covered in your plan. You may also be able to use money from a healthcare savings account to pay for them.
Portable Fans and Misters These inexpensive accessories can provide on-the-go cooling.
How to Manage Heat During Exercise
Regular exercise is important for people with MS, both for overall health and for symptom management. These tips can help you avoid overheating during exercise.
Exercising in Cooler Environments “Indoor gyms or early morning or late evening workouts can help keep you from getting overheated,” says Anderson. Water aerobics or swimming in a cool pool (less than 85 degrees) are also good options, she adds.
Water Breaks Take frequent hydration breaks during exercise to maintain fluid balance and prevent overheating.
Pacing and Listening to Your Body Avoid pushing yourself too hard. If you experience symptoms like dizziness or fatigue, stop and cool down immediately.
Cooling Strategies During and After Exercise Use cooling towels or vests during and after exercise to help lower your body temperature and reduce fatigue. A cool bath after exercise can help, too.
Be Mindful of Environmental Heat
Some foods, drinks, and medicines can contribute to overheating, as can hot environments.
Hot Beverages and Foods Be cautious with hot beverages and foods, as they can raise your internal body temperature. Opt for cooler foods and beverages in warm environments.
Saunas, Hot Tubs, and Steam Rooms Avoid using saunas, hot tubs, and steam rooms — they can significantly increase body temperature and exacerbate symptoms.
Sun Exposure Protect yourself from sun exposure by wearing protective clothing, hats, and sunscreen to prevent overheating and skin damage.
Medications and Heat Sensitivity Some common medications can increase heat sensitivity, including antidepressants, pain relievers, and overactive bladder medications. Discuss with your doctor whether any of your medications may affect your ability to regulate body temperature.
Alcoholand Caffeine Both alcohol and caffeine are diuretics, meaning they cause you to urinate more frequently, which can contribute to dehydration, particularly in the heat. Alcohol use can also increase heat sensitivity.
The Takeaway
Heat sensitivity affects up to 80 percent of people with MS and can temporarily worsen symptoms like fatigue, weakness, and cognitive difficulties.
MS symptoms flare up when you overheat because of slower nerve signal transmission and impaired temperature regulation caused by damage in the central nervous system.
Managing heat sensitivity involves practical strategies like staying in air-conditioned spaces, using cooling towels or vests, timing outdoor activities for cooler parts of the day, and staying well-hydrated.
Be proactive about cooling techniques and discuss medication side effects with a healthcare provider to reduce risk and support better symptom control.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
Panginikkod S et al. Uhthoff Phenomenon. StatPearls. October 24, 2022.
Jessica Baity, MD, is a board-certified neurologist practicing in southern Louisiana. She cares for a variety of patients in all fields of neurology, including epilepsy, headache, dementia, movement disorders, multiple sclerosis, and stroke.
She received a bachelor's degree in international studies and history from the University of Miami and a master's in international relations from American University. She graduated from the Louisiana State University School of Medicine, where she also did her internship in internal medicine and her residency in neurology.
Prior to practicing medicine, she worked in international relations and owned a foreign language instruction and translation company.
Becky Upham has worked throughout the health and wellness world for over 25 years. She's been a race director, a team recruiter for the Leukemia and Lymphoma Society, a salesperson for a major pharmaceutical company, a blogger for Moogfest, a communications manager for Mission Health, a fitness instructor, and a health coach.
Upham majored in English at the University of North Carolina and has a master's in English writing from Hollins University.
Upham enjoys teaching cycling classes, running, reading fiction, and making playlists.
