Too warm for you? Heat sensitivity explained!

Ice cream just becauseSummer has finally arrived and with it, comes a list of things you wished you knew before sunburn blasted your chest.

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 is 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.

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

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

UPDATED: June 30th, 2019


Blog Awards 2018_Winners Gold MPU

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

◾ MyTherapy: Multiple Sclerosis Blogs: 10 of the Best in 2019
◾ Ireland Blog Awards: Finalist 2014, 2015, 2017
◾ MyTherapy: Best MS Blog for Simplicity 2018
◾ Everyday Health: Top 10 MS Blog of 2018
◾ Feedspot: Top 50 MS Blog 2017, 2018, 2019

© Willeke Van Eeckhoutte and Ireland, Multiple Sclerosis & Me, 2018. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Willeke Van Eeckhoutte and with appropriate and specific direction to the original content.

15 thoughts on “Too warm for you? Heat sensitivity explained!

  1. Reblogged this on Ireland, Multiple Sclerosis & Me and commented:

    Warning signs when heat sensitivity strikes people with multiple sclerosis, and what to do when it happens.

    “Uhthoff’s phenomenon shows up 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.”

  2. Thanks for your comment, Sal. You have been through the wars so last summer. I hope this year is a little bit better for you. It’s difficult not being the best in warm weather but you have to listen to your body before it decides for you.

    1. Thank you! So sorry to hear your vision is impacted this way! Let’s hope for cooler days now! I am secretly hoping for autumn to arrive tomorrow :)

  3. Very informative! I know when I was in Ireland a couple weeks ago it was the biggest heatwave there in 30 years (or so I heard). I can’t imagine what that must’ve been like for someone with MS. What specific ‘keeping cool’ strategies, of the ones you listed, did you employ?

    1. Thanks! And you heard right, it has been the biggest for decades and definitely the longest, too. We’ve had a cooler week but now the temperatures are up again.

      Freezer ice packs (or bags of peas because they bend easily for use in the neck are fabulous, but otherwise, every single one of all of the above has been tried and tested. Because of side effects of changing DMTs three times the past four months, my body has been having a lot of trouble adjusting. Staying indoors, using fans and ice packs are my main go-to’s right now.

  4. I used to love the summers, lay out by the pool for hours, at the beach every weekend, hanging out at the boardwalks, and best of all spare of the moments road trips. Much is that has declined and I flee for shade every moment I can get. Last year summer was a huge wake up call for me. Winded up in emergency 3x in 3 months. I can still do all what I used to do just at a lower level, much lower. Thanks for sharing.

    1. Thanks for your comment, Sal. You have been through the wars so last summer. I hope this year is a little bit better for you. It’s difficult not being the best in warm weather but you have to listen to your body before it decides for you.

  5. A truly interesting and informative article 🙄and a sincere thank you for following my blog /website, muchly appreciated, I hope you enjoy reading my humble writings and I’m from Geelong, Australia. Cheers Ivor 🌏

    1. It’s entirely my pleasure Ivor! Do keep writing, your words are heartfelt and inspiring so I will definitely return for more! I hope things are well at the southern border of Australia!

      1. Nice to hear from you 😊, and I hope you are keeping well over there, and I hear your area is in for another hot spell, so look after yourself and I’ll be thinking of you 😙

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