Why a rise in your body temperature can trigger MS symptoms

  Yoga in the sun

Ireland it seems, is going through the most mundane summer since I moved to Ireland 22 years ago. No heat waves just yet, not even a prolonged period of ‘just’ warm weather. In fact, here I am, wearing wooly winter house boots because my feet and ankles feel like they’re wrapped in snow and cold water.

But, across the big pond, America is going through a heat dome, something that sounds fancy, but must be awful if you happen to live under it. If news reports are to be believed, Europe will fall under the same conditions quite soon.

Oh, joy.


If you have multiple sclerosis and hot or cold temperatures trigger symptoms, here are some tips to avoid worsening of existing symptoms.

Heat sensitivity is, of course, an uncomfortable sensation many people struggle with and is, therefore, not a symptom solely attributed to MS. The difference from other illnesses lies in how heat affects the central nervous system.

Uhthoff’s phenomenon occurs when changes in body temperature make a person’s existing MS symptoms worse, even a rise of 0.25°C to 0.5°C in the core body temperature is enough to cause upsetting symptoms in those living with MS.

Because of nerve damage in MS, symptoms will depend on the severity and the part of the nervous system that is damaged. Excessive heat sensitivity in MS causes temporary worsening of existing symptoms and more worryingly, can also cause new symptoms.

As such, physical exercise or being in a warm environment for a longer time period should be monitored. Although no nerve damage will occur because of an increase in temperature, you may still feel like you just entered a relapse.

A flare-up of existing symptoms caused by another medical event is therefore called a ‘pseudo-exacerbation’ or ‘pseudo-relapse’.

Studies have shown that heat sensitivity is a key clinical factor in MS heat sensitivity is a key clinical factor in MS.

See below for causes, how to tackle heat sensitivity and know the risk factors before it’s too late.


  1. Temporary exacerbation of existing MS symptoms and new disturbing symptoms when exposed to elevated temperatures,
  2. ‘Pseudo-exacerbation’ of the symptoms as an increase in temperature as such does not cause any nerve damage,
  3. Disturbance or block in the normal physiological nerve conduction mechanisms. Demyelination not only causes slowing of nerve impulse conduction along the affected nerve fibres but also linked to a phenomenon called Frequency Dependent Conduction Block,
  4. Premature fatigue when people with MS are exposed to even a slight increase in temperature,
  5. Energy down to a bare minimum,
  6. Recharging very hard to achieve,
  7. Intense limb weakness,
  8. Visual problems,
  9. Neuropathic pain due to damage caused to the thalamus and the spinothalamic-cortical pathways leading to thermo-regulatory dysfunction,
  10. Worsening numbness,
  11. Pins and needles,
  12. Dizziness,
  13. Cognitive dysfunctions like memory problems,
  14. Judgment difficulties,
  15. Concentration difficulties,
  16. Language comprehension,
  17. Slurred speech,
  18. Nauseous and a feeling of fainting about to happen.


60 to 80% of people with MS have excessive heat sensitivity issues.


  1. A slight increase in core body temperature (0.25°C to 0.5°C) raises the core body temperature because of nerve damage in MS patients.
  2. Nerve transmission requires more energy to work in the heat, and even more when there is demyelination.


  1. Physical exercise,
  2. Warmer environment,
  3. Cooking in front of a hot oven and over a hot stove,
  4. Eating or drinking hot food and/or fluids,
  5. Warm indoor and other heat-inducing surroundings,
  6. Sunbathing or being outdoors in hot weather,
  7. Bathing in hot water,
  8. Strong emotional responses or experiences,
  9. Fever,
  10. Use of a hairdryer,
  11. Hormonal changes in women,
  12. Hot flashes during menopause.

How to handle?

  1. Avoid working outside during the warmest hours of the day (11am to 4pm),
  2. Seek out shade and/or carry an umbrella wherever you go,
  3. Take lukewarm showers instead of cold ones. Taking cold showers only help you keep cool for a short period of time as your body’s core will warm up because of reduced heat loss from the body without skin blood flow. Some minutes later, we feel hot again. But, a warm sensation on the skin will lead to increased blood flow to the skin, increasing heat loss from the body,
  4. Keep your head and neck area cool with a wet, cool towel from the freezer,
  5. Stay well-hydrated,
  6. Use hand-held fans like fan-topped spray bottles to cool down your face,
  7. Use a desk-fan at work,
  8. Add short breaks to your schedule to avoid full depletion of your energy levels,
  9. Keep your freezer stocked with small ice packs, cold water bottles, neck wraps,
  10. Wear cooling vests or bras with cooling pads in,
  11. Wear loose-fitting, breathable white clothes in layers,
  12. Drink ice water with lemon, or cold iced tea, avoiding anything sugary,
  13. My Cooling Towel, a $15 to $20 scarf-shaped piece of fabric that, once dampened, displays unique cooling properties. It can be draped around your neck, wrapped around your head or wrists, or laid across your legs to offer maximum cooling on the hottest parts of your body.

When to seek medical intervention?

Medical intervention isn’t necessary for symptoms of Uhthoff’s. If you’ve experienced it before, you’ll know what to expect. But it’s easy to confuse heat-related symptoms with other medical emergencies.

Seek medical attention if:

  1. You’ve never experienced heat-related symptoms of MS before,
  2. You’re uncertain that your symptoms are Uhthoff’s or MS-related,
  3. You have accompanying symptoms unrelated to MS,
  4. Your symptoms don’t improve after you’ve cooled down.

Is emigrating to a climate that suits you better the answer?

While heat and humidity can trigger a wide range of MS-related symptoms, so can cold weather. High humidity or cold temperatures can trigger involuntary muscle spasms or stiffness, called spasticity.

If you have heat- or cold-related symptoms of MS, it’s best to avoid exposure to any extreme temperature. If you’re thinking of relocating for health reasons, it’s a good idea to spend some time in a different climate first to see if it makes a difference.

(In my case, living in Ireland in a more temperate climate helps my heat sensitivity, as summer temperatures in Belgium are testing for me)


If you or a loved one has MS, have a plan in place for staying cool, but also be ready for the unexpected. For example, a car break-down could leave you stranded with no way to cool down. A battery-powered spray bottle fan filled with water and tossed in the trunk might be all you need to keep Uhthoff’s Syndrome at bay.

History of Uhthoff’s Phenomenon/Sign

Among the various symptoms of MS, Wilhelm Uhthoff in 1890 described the peculiar phenomenon of ‘temporary worsening of symptoms with exercise’ in optic neuritis patients. Optic neuritis is a condition affecting the eyes. It is a common problem for many people with MS.

Uhthoff noticed that visual symptoms were aggravated when people with MS performed exercise. While he attributed exercise to be the aetiology of this problem, it was later realised that any action or condition that increases the core body temperature can worsen the symptoms in MS patients, and therefore not just those related to vision. This is called the Uhthoff’s phenomenon or Uhthoff’s sign.

MS causes nerve damage and nerves relay information to and from the brain. With 50+ different and possible symptoms associated with MS, it’s hard to pin down which is the

most annoying. While you will not have every single one on the list, some will have a larger impact on your daily life than others.

More info

MS & Uhthoff’s Phenomenon: Coping with Heat Sensitivity, MyTherapy

Multiple Sclerosis Patients Especially Sensitive to Heat, Healthline

Temperature sensitivity, Multiple Sclerosis Trust

Uhthoff’s Phenomenon, ScienceDirect

While you’re here, why not check out these pages?

MS, a riddle wrapped up in an enigma

Heat sensitivity and multiple sclerosis: is it autumn yet?

Body image and MS: how many selfies do you have?

Sensory MS symptoms: the hair that isn’t there

About Vikings, vitamin D and searing multiple sclerosis

Media, stop calling it a cure when hasn’t even been clinically trialled yet!

The duality of MS

When life with MS is like The Clash’s ‘Should I Stay or Should I Go’

UPDATED: June 29th, 2024

2018 Winner Best Blog Post, Ireland Blog Awards by Ashville Media Group, Dublin, Ireland2018 Winner Best Blog Post, Ireland Blog Awards by Ashville Media Group, Dublin, Ireland2018 Winner Best Blog Post with ‘3443 Needles’, Blog Awards Ireland, Ashville Media Group, Dublin, Ireland

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◾ MyTherapy: Best MS Blog for Simplicity 2018

◾ Blog Awards Ireland: Finalist 2017, 2015, 2014; Winner Best Blog Post 2018 (Awards competition discontinued from 2019 onwards)

© Willeke Van Eeckhoutte and Ireland, Multiple Sclerosis & Me, 2011-2024.

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