Why Heat Makes MS Symptoms Worse (and 4 Things That Finally Helped)

Heat makes MS symptoms worse for most of us — and for years, it made mine so much worse that I dreaded every Idaho summer. I was lucky in that debilitating fatigue was never really my issue with MS. Instead, heat had its own way of getting me.

I remember afternoons out here on the homestead when I’d walk from the garden to the house and by the time I got to the porch, my face would turn bright red and my eyes would start to black out. My legs would get so weak I could barely walk — like my whole body was shutting down. It would take hours to recover. I used to think I was having a relapse every single time the temperature climbed. It scared me every time.

It isn’t a relapse. And in 2015, mine disappeared — though it didn’t happen overnight, and it wasn’t from any one single thing.

In March of that year, I made one big change: I stopped following a strict MS diet. Not because it was doing anything wrong, but because I wasn’t seeing improvement from it anymore, so I decided to stop following someone else’s rules and start actually listening to my own body instead.

That’s when I discovered some of the foods I’d been eating because they were supposed to be “healthy” were working against me. It turned out I’m sensitive to histamine — foods like sauerkraut and leftovers that have sat too long still have to be portioned carefully for me even now. I was also drinking lemon water every day because it’s supposed to be good for you, and every single time, I’d slightly lose my voice and have to keep clearing my throat.

Around that same time, I saw a functional medicine provider, who had my vitamin D levels checked. Mine came back on the low side of “normal” — low enough to matter, which I get into more in my Vitamin D Healing Guide. He also had me start eating more flaxseed, something I still do to this day (more on that here: Flaxseed post).

Then in late June, once the weather started warming up, I noticed the heat wasn’t affecting me the way it always had. I honestly didn’t believe it. I tested it over and over, waiting for it to catch up with me. It never did.

I’m still not entirely sure which piece made the biggest difference, or whether it was the combination of all of it. Around that same stretch of time, I was also making sure I drank enough water, slept well, and — the hardest part by far — worked on my stress. Stress has always set me back more than almost anything else. I didn’t just try to lower my everyday stress levels; I worked hard on how I responded to stress, and how I talked to myself when things got hard. That part took a long time to change. Every time I caught myself thinking something unkind about myself, I made myself stop.

A lot of my symptoms improved after that stretch. Not all of them — I still live with some, and I’m not claiming to be cured. But between eating in a way that actually works for my body, staying active, and how I treat myself, I’m in a genuinely good place now, MS and all.

I share all of that not to promise the same thing will happen for you, but because I know how much it used to shape my summers when heat makes MS symptoms worse, and I want you to have the tools that helped me through the many years it was a real problem — tools that still help a lot of people managing this right now.

What’s Actually Happening When Heat Hits You

Heat makes MS symptoms worse because of biology, not because you’re doing something wrong. MS damages the protective coating (myelin) around your nerves, and damaged myelin is far more sensitive to temperature changes than healthy myelin. Even a small rise in your core body temperature — from a hot day, a hot bath, exercise, or a fever — can temporarily slow down the nerve signals traveling along those damaged areas. That temporary slowdown is what causes symptoms to flare up or old symptoms to resurface.

This has an actual name: Uhthoff’s phenomenon. Researchers have been documenting it for decades. The key word is “temporary.” Once your body cools back down, the nerve signals go back to normal. The symptoms settle back down with them.

The worsening is almost always in symptoms you’ve already had before, not brand-new ones. And it goes away once your core temperature comes back down.

Studies have also found that heat and cold sensitivity are one of the most common triggers people with MS recognize in themselves, closely tied to fatigue and other symptoms. That probably sounds familiar if a summer afternoon has ever wiped you out completely. And research on exercise specifically backs up what a lot of us learn through trial and error: cooling down before and during activity measurably reduces how much heat affects your symptoms.

Knowing all of this changed how I approached summer. It’s not willpower. It’s not “pushing through.” It’s a nervous system responding to temperature exactly the way research says it will — and cooling down is the actual, physical fix.

4 Things That Help When Heat Makes MS Symptoms Worse

This is the toolkit I leaned on for years, and it’s still what I recommend when heat makes MS symptoms worse for you too.

Cool your body proactively, not reactively. Waiting until you feel bad means you’re already behind. I keep a rotation of go-to cooling products on hand from spring through early fall, and I use them before I head outside to garden or do chores, not after I’ve already overheated.

Hydration matters more than people think. Dehydration makes heat sensitivity worse, and it’s easy to under-drink when you’re not sweating heavily or when you’re limiting fluids for other reasons. I go into more detail on how much and what kind of hydration actually helps with MS symptoms here.

What you eat and drink can help you cool down from the inside. This is honestly one of my favorite parts of managing this naturally, because it means summer doesn’t have to be all restriction — it can be genuinely enjoyable. My cooling foods and cold drinks for MS posts cover what I actually reach for on hot days, straight from my own kitchen and garden.

Build a longer-term plan, not just hot-day fixes. The workbook I put together this year, Better Days: A 90-Day Quality of Life Workbook, has a whole section on tracking your personal triggers — including heat — so you can see your own patterns instead of guessing. It’s the tool I wish I’d had decades ago, back when I thought every hot day meant a relapse.

The Bottom Line

Heat makes MS symptoms worse because of how damaged myelin conducts nerve signals when your core temperature rises — not because something new is going wrong. Once you understand that, and you build a cooling strategy that fits your life, summer stops being something to survive and starts being something you can actually plan for.

It took me a long time to get here. I hope this post gets you there faster than it got me.

Could Something Else Be Contributing to Your MS Symptoms?

Heat is just one piece of the puzzle. My free Find Your Root Cause of MS guide walks you through four common patterns—nervous system, inflammation, energy, and gut health—so you can discover where you may want to start.

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📌 Living with heat-sensitive MS symptoms?

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