“If I’m hot, I’m weak,” one MyMSTeam member said. “Any slight warmth over 70 F, and I reel. Heat sucks,” shared another.

Many people with multiple sclerosis (MS) are sensitive to heat and changes in body temperature. Even a quarter- or half-degree change in core body temperature can temporarily trigger MS symptoms. Environments others might not think twice about — a humid backyard, stuffy room, or hot shower — can make MS symptoms worse. This is called Uhthoff’s phenomenon.

The effects of heat on MS symptom flare-ups are so well established that before the invention of MRI, doctors used to give a hot bath test to people they believed had MS. If the person’s neurological symptoms suddenly flared in hot water, the physician would presume their diagnosis was correct.

Thankfully, tests like those are unnecessary today. With some planning and preparation, people with MS can use strategies to avoid the complications of heat sensitivity.

What Does MS Heat Sensitivity Feel Like?

Members of MyMSTeam often discuss heat sensitivity and temperature changes.

“Don’t have a problem being cold,” one member said. “It’s the heat that shows me MS is still in charge.”

Heat can affect energy levels and mobility. One member described hot days as, “Like I am trying to walk through Jell-O and everything hurts.”

Another said, “I get fatigue really bad, and brain fog.”

“I also get too hot and have an almost heatstroke-like reaction, and I get dizzy and nauseous,” said a third member.

Many MyMSTeam members say the heat limits their productivity. “I am constantly overheating, it makes it difficult to do anything” one member shared.

Another said, “Hot weather, I seem to tire faster, so I take a little more time doing things.”

One member said a trip to a hot vacation destination put them in the hospital: “Heat and humidity are my enemies! I went to a family reunion, and the heat and humidity made my MS flare up so bad. I had a horrible MS hug, felt like I couldn’t breathe, and lost consciousness.”

MS and Heat-Intolerance Symptoms

MS symptoms most commonly associated with heat intolerance include:

• Fatigue
• Pain
• Difficulties with concentration
• Blurred vision
• Muscle weakness or spasticity

One MyMSTeam member shared that they experience worsened muscle symptoms in the heat. During heat waves, they wrote, “The good old legs decide to fight me big time.”

MS symptoms caused by heat sensitivity are usually temporary. They generally go away once the body cools down.

It’s important to be aware that relapsing symptoms or flares caused by heat can also create secondary health risks. As one team of researchers explained, heat sensitivity in people with MS is strongly correlated with fatigue. When combined with memory issues and muscle weakness, feeling tired and being sensitive to heat can increase the risk of accidental falls.

Read about unusual sensations and MS.

How Can Heat Make MS Symptoms Worse?

In people with MS, the body’s immune system attacks the central nervous system, causing inflammation and stripping the nerves of their myelin (protective coating). This process, known as demyelination, leaves the nerves vulnerable and reduces their ability to transmit electrical signals to the brain.

Research indicates that when a person with MS experiences an uptick in core temperature, neural conduction (the passing of messages along nerve fibers) slows down. In some cases, it may be blocked entirely. This can cause a worsening of MS symptoms. The severity of the flare-up depends on the extent of a person’s demyelination and how much their core temperature has heated up.

How Does Having MS Affect Your Body Temperature?

MS can negatively affect a person’s ability to maintain a healthy body temperature. If a person develops a lesion in an area of the brain that regulates core temperature or cooling responses (such as sweating or circulation), they may not be able to adjust to a warmer environment.

Heat intolerance, or heightened sensitivity to heat, is one of the most common symptoms of MS. This condition affects between 60 percent and 80 percent of people with MS. These individuals may experience a pseudo-exacerbation (temporary symptom flare) if their core body temperature rises. Warm environments can trigger a temporary worsening of MS symptoms, as can exercise and fevers caused by illness or infection.

You Can Take Steps To Manage Heat Sensitivity

Heat sensitivity can be managed to help prevent heat-induced symptoms of MS. You can also take steps to control symptoms as they come on to help relieve a temporary flare from heat as quickly as possible.

Here are some ways to manage heat intolerance and improve your quality of life.

1. Cool Down Right Away if Heat-Intolerance Symptoms Start

When you’re in the middle of a heat-prompted MS flare-up, you can take a few immediate actions to cool yourself down. You might try:

• Drinking cold drinks
• Sucking on ice cubes or popsicles
• Taking a cooling shower or bath
• Misting yourself with ice water
• Eating a cool dessert and light meals

If you opt for a cooling shower or bath, be sure not to shock your system with cold water too fast. Start with lukewarm water, then slowly lower the temperature.

Get ideas for healthy snacks for MS.

2. Maintain a Comfortable Schedule for Daily Activities

You can reduce your future risk of pseudo-exacerbations by creating a schedule that takes heat and temperature sensitivity into consideration as much as possible. Try avoiding activities outside during the heat of the day. Be sure to take your time with everyday chores or everyday activities to help prevent overheating. Plan ahead for the extra time you need to manage activities at a comfortable pace.

It can be helpful to let family members and friends know that you may need to adjust social activities to accommodate your heat sensitivity.

Talk to your doctor or neurologist for advice on protecting yourself from heat that may trigger symptoms during daily activities.

3. Be Mindful of When and Where You Exercise

If you want to work out, do so in a cool environment. Avoid hot or stuffy rooms. If you plan any outdoor activity, try to do it during the cooler early morning hours or in the evening.

Don’t overexert yourself, and take regular breaks. As one MyMSTeam member shared, “My physical therapist noticed one day that I don’t rest between activities. I just push on through. We had a serious talk about giving myself permission to rest.”

Be sure to have water on hand while exercising. Consider setting aside 30 minutes after your workout for a cooling bath or shower. This can help you safely lower your core temperature and keep cool.

People with heat sensitivity should avoid hot tubs or saunas at the gym or recreationally.

4. Use Climate Control at Home

If you live in a hot or humid climate, you may want to consider investing in air conditioning or fans. These will help you regulate the air temperature of your home and limit your chance of experiencing environmental heat triggers. Even an air conditioner in one room can provide you with a place to stay cool.

“I bought a personal and portable AC unit for my household,” one MyMSTeam member shared. “The really nice thing about it is that I can take it anywhere with me, so that I can have a way to beat getting heat stroke/overheated.”

5. Consider Cooling Clothing

If you find lightweight garments and breathable clothing aren’t enough to help you cope with the heat, you may consider specialized cooling clothes. These garments are often specifically made for people who have MS. They contain a gel-like substance that can be chilled before use and provide cooling effects for several hours or days. These cooling products come in a variety of forms, including neck wraps, bandanas, hats, and wristbands.

If you need more cooling support than gel-lined clothing can provide, you may want to try a cooling vest. These vests resemble waistcoats and feature battery-powered cooling packs that keep your torso cool. Because cooling vests are often designed for athletes, they usually stay comfortable even during vigorous physical activity. Research indicates that people with MS who use cooling vests may be able to walk farther and longer without fatigue than their peers.

“I have a cooling vest and have fans on me all the time,” one MyMSTeam member said.

Another shared a creative way to achieve a similar effect: “I was having a very hard time getting a cooling vest. So I went to the secondhand store and got a fishing vest, and packed it with ice packs. LOL! My vest lives in the freezer.”

Everyone with MS experiences symptoms differently, and what works for one person may not be suitable for another. It can be a trial-and-error process to find what works best for you.

Talk With Others Who Understand

On MyMSTeam, the social network for people with MS and their loved ones, more than 206,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS. You can ask questions, provide insights, and even just make conversation with people who truly understand what it’s like to live with MS.

Does heat affect your MS symptoms? Do you have a tip to share on staying cool? Start the conversation by leaving a comment below or making a post on your Activities page.