Some days, the weather is just the weather. For someone living with multiple sclerosis, heat can be something else entirely.
A warm afternoon can change how your body feels. A hot shower can make familiar symptoms suddenly more noticeable. Exercise that normally feels manageable can leave you unexpectedly weak, tired, or unsteady.
I was diagnosed with MS at 23, and one of the things I’ve learned over the years is that sometimes the hardest part isn’t the heat itself. It’s explaining why something so ordinary can change the entire shape of your day.
When Temperature Becomes Part of the Plan
Before MS, I never thought about temperature as something I needed to manage. Hot weather meant summer, a hot shower meant a hot shower, and exercise meant getting warm and sweaty. Those things were ordinary, and I didn’t give them a second thought.
MS changed the way I experience them.
Now temperature can become part of the day’s calculation. How long will I be outside? How hot will it be? Is there somewhere cool nearby? Will I still have enough energy afterward?
Those are questions I never used to ask, but they’ve become part of understanding how my body responds to heat.
Heat sensitivity occurs when an increase in body temperature temporarily worsens existing MS symptoms. This is often called Uhthoff’s phenomenon. Heat can interfere with nerve signals travelling through areas already affected by MS, making symptoms more noticeable.
For some people, that means heavier legs, increased weakness, blurred vision, numbness, tingling, balance problems, or difficulty concentrating. The frustrating part is how quickly things can change. You may feel relatively fine one moment and noticeably different after your body temperature rises.
And the trigger doesn’t have to be a hot summer day. A hot shower, crowded room, heated building, physical activity, or fever can raise body temperature enough to make symptoms worse.
That’s why heat sensitivity deserves attention throughout the year, not just during summer.
When Being Active Gets Complicated
Movement has always been an important part of my identity. I played sports, became a physical education teacher, and coached. So the idea that exercise could temporarily make some of my symptoms worse was difficult for me to understand.
Exercise itself isn’t something people with MS necessarily need to avoid. Regular physical activity can be beneficial, but getting overheated may temporarily worsen symptoms for someone who is heat sensitive.
That means the goal isn’t necessarily to stop moving. It may be finding different ways to move without allowing your body temperature to rise too much.
For some people, that means exercising during cooler parts of the day. For others, it might mean taking more breaks, choosing a cooler environment, wearing breathable clothing, or trying water-based activities.
I had spent years believing that if something was difficult, I needed to push harder. That approach served me well in many parts of my life, but MS made it much more complicated.
Sometimes pushing harder doesn’t solve the problem. Sometimes changing the conditions makes more sense.
And when you’ve built so much of your identity around movement and physical capability, that isn’t always an easy adjustment.
What Other People Don’t See
Sometimes heat sensitivity doesn’t completely stop you from doing something. It simply changes the experience.
A walk becomes shorter, an outdoor event requires more planning, a shower needs to be cooler, or an afternoon outside means finding shade. A day that looked simple on the calendar suddenly requires more preparation.
That preparation can be invisible to everyone else. They see you arrive and participate, but they may never see the decisions that made participation possible.
And if you suddenly need to sit down, leave early, or change your plans, they may have no idea why.
What I want people to understand is that the change is real, even when you cannot see the cause.
A person with MS doesn’t need to look dramatically different for heat to have changed what their body is capable of doing in that moment.
Heat Sensitivity and MS Relapses: Understanding the Difference
Heat sensitivity generally causes a temporary worsening of existing MS symptoms without causing new inflammatory damage. Once body temperature returns to normal, those symptoms usually improve.
A true MS relapse involves new or worsening neurological symptoms that last at least 24 hours, in the absence of fever, infection, or another explanation, following a period of stability. A healthcare professional needs to assess whether those symptoms represent a relapse.
That doesn’t mean every symptom change should automatically be blamed on heat.
If symptoms are new, significantly worse, persist after cooling down, or occur alongside fever or signs of infection, contact your healthcare professional or MS team. You don’t need to wait 24 hours to seek advice about concerning symptoms.
Understanding your usual patterns can be helpful, but you shouldn’t have to diagnose yourself.
Practical Ways to Manage Heat Sensitivity
There isn’t one strategy that works for everyone, but there are practical ways to reduce the effects of heat.
Keep your surroundings cool. Air conditioning, fans, shade, and cooler rooms may help. At home, closing curtains during the hottest part of the day can reduce heat entering a room.
Pay attention to timing. Outdoor activities and errands may be easier during cooler parts of the morning or evening. Sometimes changing the time of an activity makes a surprising difference.
Think about clothing and cooling. Loose, breathable clothing, cool drinks, cooling neck wraps, or cooling vests may help some people. A cool shower can also help bring body temperature down.
Adjust physical activity. Shorter sessions, planned breaks, cooler environments, and water-based exercise may make activity more manageable. If you’re unsure how to exercise safely with your symptoms, speak with a qualified healthcare professional.
The goal isn’t to organize your entire life around the temperature. It’s to understand which adjustments allow you to keep doing the things that matter.
The Freedom to Do Things Without Thinking Twice
There’s an emotional part of heat sensitivity that is harder to explain. You can understand exactly why something is happening and still feel frustrated that you have to think about it.
Sometimes I miss the simplicity of doing something without calculating the consequences first.
Before MS, I could decide to go outside and go. I could exercise without wondering how my body temperature might affect me afterward. I could take a hot shower without thinking about whether I’d feel different when I stepped out.
Those small freedoms are easy to take for granted until they become things you have to consider.
I don’t think acknowledging that loss means giving in to it. It simply means being honest about what changed.
For years, I measured a good day by how much I could accomplish. I was used to pushing myself, meeting challenges, and finding a way to get things done.
But living with MS has made me question whether accomplishment always needs to look the same.
Maybe I leave an event earlier, move an activity indoors, or take a break when everyone else keeps going. None of those decisions means I’ve given up.
I still love being active, and I still don’t particularly enjoy having MS interfere with my plans.
But after all these years, I’m getting better at changing the conditions instead of abandoning the plans.
Related reading: MS fatigue management tips | MS and sleep
References and Further Reading
The medical information in this article is supported by the following resources. Personal reflections are based on my experience living with MS.
- MS Canada. Symptoms of MS, including Uhthoff’s phenomenon (heat intolerance).https://mscanada.ca/intro-to-ms/ms-symptoms
- MS Trust. Heat sensitivity and MS (Uhthoff’s phenomenon).https://mstrust.org.uk/a-z/heat-sensitivity-uhthoffs-phenomenon
- MS Society (UK). The effects of temperature on MS.https://www.mssociety.org.uk/about-ms/signs-and-symptoms/effects-temperature-ms
- National Institute for Health and Care Excellence (NICE). Multiple sclerosis in adults: management (NG220).https://www.nice.org.uk/guidance/ng220
