Heat sensitivity in MS is not something I learned about from a textbook. I learned about it by getting too hot and discovering that my body suddenly stopped working as well as it had a few minutes earlier.

For me, heat can affect my eyesight, balance, strength and fatigue. Humidity can be even more debilitating than dry heat. Sometimes the change is surprisingly rapid.

Only later did I learn that this experience has a name: Uhthoff’s phenomenon.

Looking back, I can remember incidents from long before my MS diagnosis when heat affected me in ways I couldn’t explain. I cannot prove what caused those experiences, but after more than 30 years of living with MS, I certainly recognise the pattern now.

What Heat Sensitivity in MS Feels Like to Me

When most people think about body temperature, they probably think about whether the house feels comfortable or how hot they become during exercise. With MS, I have learned to pay rather more attention.

A rise in temperature can make existing neurological problems temporarily more noticeable. The MS Trust’s information on temperature sensitivity explains that changes in body or skin temperature can temporarily worsen MS symptoms.

In my case, vision has provided some of the clearest examples.

The Garden Taught Me Something Was Wrong

In the early 1990s, shortly after moving into our current house, there was plenty of work to do in the garden. One sunny afternoon I decided to dig what was intended to become our vegetable patch.

Digging is hot work.

As I became warmer, my eyesight deteriorated. Everything became blurred and darker. The visual disturbance made me dizzy and nauseous, so I stopped, sat down and had a coffee.

As I cooled, my vision returned.

I went back to digging. I became hot again — and my eyesight deteriorated again.

This was before my MS diagnosis in 1994. At the time I didn’t know what was happening. Looking back at the signs before my MS diagnosis, it is one of those experiences that makes considerably more sense with hindsight.

A Much Earlier Memory of Heat

I also have a vague childhood memory from the late 1960s. I came home from primary school on an unusually warm afternoon and couldn’t get into the house because my parents were still at work.

Normally, that wouldn’t have bothered me. But I remember finding the heat oppressive and trying to shelter beneath bushes in the garden because I felt so unwell.

Was that MS? I have absolutely no way of knowing, and I would not claim that it was. One childhood incident proves nothing.

It is simply a memory that became more interesting after decades of experiencing a very definite relationship between heat and my neurological symptoms. That distinction matters because many symptoms associated with multiple sclerosis can have numerous other causes.

Uhthoff’s Phenomenon and Worsening Neurological Symptoms

Uhthoff’s phenomenon describes a temporary worsening of existing MS symptoms when body temperature rises. It is named after Wilhelm Uhthoff, a German ophthalmologist who observed worsening visual problems after exercise in people with optic neuritis.

The important word is temporary.

The MS Society’s explanation of temperature and MS notes that heat can affect balance, weakness, fatigue, vision and sensation, among other symptoms.

Why Rising Body Temperature Can Affect MS Symptoms

MS damages myelin, the protective covering around nerve fibres. Those damaged pathways may already have difficulty transmitting signals efficiently.

Add heat and the transmission of those signals can become less effective. Consequently, a symptom that was already present may temporarily become more noticeable.

For me, that might mean blurred vision, dizziness, weakness or difficulty standing.

Heat Does Not Necessarily Mean New Damage

This distinction can be reassuring.

Temporary symptom changes caused by heat exposure are not usually evidence that MS has suddenly caused fresh neurological damage.

When the body cools, nerve transmission improves again and the symptoms should move back towards their previous level.

That is very different from assuming that every bad afternoon means the MS itself has progressed.

When a Change Deserves Medical Advice

I would still never dismiss a new or unusual symptom simply because the weather happens to be warm.

If symptoms are new, significantly worse than usual, persist after cooling down, or occur alongside fever or signs of infection, that is a good reason to speak to a GP or MS team.

Living with MS teaches you to recognise patterns, but recognising your usual pattern is not the same as diagnosing every change yourself.

Heat Triggers Go Far Beyond Hot Weather

A blazing summer day is an obvious problem, but outside temperature is only one way of becoming overheated. Exercise, fever, warm rooms, hot showers and baths can all raise body temperature.

For me, humid weather can be particularly unpleasant. I can sometimes cope reasonably well with dry warmth but find a muggy day thoroughly draining.

Why My Long Hot Baths Had to Go

I used to love a long, hot soak in the bath. Unfortunately, my idea of a luxurious bath and my nervous system’s idea of a sensible temperature are not remotely compatible.

I learned that lesson rather dramatically.

On one occasion I ignored what experience had already taught me and had a piping-hot bath. When I tried to get out, I could barely stand.

In fact, I couldn’t stand.

I simply sank to the floor and lay there, naked, for about fifteen minutes until I had cooled sufficiently to get myself moving again.

It was not one of my more dignified moments, but it demonstrated the effect perfectly. Nothing permanent had suddenly happened to my legs. Getting too hot had temporarily made an existing neurological weakness much worse.

Exercise Can Raise Temperature Too

Exercise deserves a more balanced discussion because avoiding overheating should not mean avoiding movement.

For several months I attended a sedentary exercise class where people of different ages and abilities took part in gentle guided exercise. I used the rowing machine and exercise bikes and, if anything, found the class insufficiently challenging.

Curiously, overheating wasn’t a problem there.

The classes ended with the Covid lockdown in March 2020 and never restarted.

Gardening was another matter entirely. Digging could raise my temperature enough to affect my eyesight, whereas controlled indoor exercise did not.

That taught me not to think of exercise itself as the enemy. The relevant question is how much heat a particular activity generates and how my body responds. Gentle movement also forms part of how I approach my morning routine with multiple sclerosis.

Managing Overheating and Temperature Changes With MS

I haven’t discovered a magical solution to heat sensitivity. Mostly, I have learned to recognise my limits and stop pretending they don’t exist.

That means avoiding very hot baths, wearing loose clothing, choosing short-sleeved T-shirts and, when necessary, shorts. I appreciate that an old man in shorts may not be the height of sartorial elegance, but sometimes practicality wins.

I have never been particularly convinced by cooling shirts or cooling tops for myself. Other people with MS find cooling garments helpful, which illustrates an important point: what works for one person may not suit another.

Rising body temperature affecting multiple sclerosis symptoms can temporarily make problems such as fatigue, blurred vision, weakness and poor balance more noticeable.

Learning When to Stop Before Heat Stops Me

I still enjoy sitting in the sunshine. I simply cannot sit there indefinitely.

After perhaps five or ten minutes, I usually know that it is time to find some shade. I don’t regard that as surrendering to MS. It is simply information my body has given me repeatedly, and I have finally learned to listen.

The same principle applies to physical activity. If my vision begins to blur, my balance deteriorates or weakness suddenly increases as I become warmer, pushing harder is unlikely to prove anything useful.

Sometimes the sensible response is remarkably uncomplicated: stop, sit down, cool off and give my nervous system time to recover.

That same willingness to adapt applies elsewhere in my journey of living with MS. Adaptation isn’t about abandoning everything you enjoy. Often it means finding another way to continue doing it.

Recognising My Own Combination of Symptoms

Heat does not affect one isolated part of my MS. Vision can deteriorate. Balance can become less reliable. Fatigue can increase and my legs can become less cooperative.

That overlap is one reason individual symptoms can be difficult to separate. My experience of restless and involuntary leg movements, for example, is explored separately in my experience of jangly legs.

Heat sensitivity has become easier to live with because I now understand what is happening. When my symptoms worsen after I become hot and then improve as I cool, I recognise a familiar pattern rather than immediately wondering whether something new has gone wrong.

Heat Sensitivity in MS Is a Pattern I Have Learned

After decades with MS, heat sensitivity in MS has become another part of understanding how my particular nervous system behaves.

The hot childhood afternoon remains only a curious memory. The repeated visual problems while digging before diagnosis are harder for me to dismiss. The bath episode was unmistakable. Together, they form part of my own history, but they should not be mistaken for a diagnostic checklist.

Uhthoff’s phenomenon helps explain why rising body temperature can temporarily worsen existing neurological symptoms. More importantly for everyday life, understanding that relationship has taught me when to stop, cool down and allow my body to recover.

Having heat sensitivity does not mean that you have MS, and a new or persistent neurological symptom deserves proper medical advice rather than self-diagnosis.

Heat sensitivity in MS can temporarily worsen existing symptoms when body temperature rises, but they usually improve again as the body cools.

While heat sensitivity is no laughing matter, there is always room to be light-hearted.

There is no single experience of MS. MyMSisMe describes one experience while using reliable evidence to explain the wider picture.