MS and heat
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About three-quarters of people with multiple sclerosis (MS) find their symptoms get worse in response to heat. This may be triggered by hot weather, increases in body temperature caused by vigorous physical activity, or an infection-induced fever.
MS-related heat intolerance is sometimes referred to as Uhthoff’s syndrome, as it was first formally described in the late 1800s by Wilhelm Uhthoff, a German neuro-opthamologist. Uhthoff noticed some of his patients’ symptoms worsened when they exercised. The term can cover MS symptoms that worsen with increases in body temperature, although it more commonly is used for worsening vision problems in MS.
What causes heat intolerance in MS?
In MS, inflammation in the nervous system causes damage to the myelin sheath, a fatty coating around nerve fibers that helps them send electrical signals. This damage and myelin loss (demyelination) impair the nerves’ ability to send electrical signals.
Heat intolerance in MS arises because changes in body temperature can affect the speed at which electrical signals travel along nerves — and that rate of speed is already slower in demyelinated nerves. Even a slight increase in core body temperature, as low as half a degree Celsius (or 0.9 degrees Fahrenheit), can further interfere with electrical signals from demyelinated nerves. This temperature dysregulation ultimately leads to a worsening of MS symptoms in response to heat.
Sometimes MS can cause damage to the parts of the brain responsible for regulating body temperature, for example, by governing sweating and shivering. This also can contribute to temperature sensitivity in MS.
What does MS heat sensitivity feel like?
When the weather is very hot or humid, most people tend to feel symptoms of heat exhaustion, which include headaches, dizziness, loss of appetite, a faster heart rate, and increased sweating.
Under these climate conditions, people with MS also can experience a temporary worsening in their disease symptoms, which, together with heat exhaustion, can pose significant challenges in their normal activities.
This exacerbation in symptoms also can be felt in other situations leading to overheating, such as having a fever, taking a hot bath, sunbathing, or doing intense exercise.
“Heat is kryptonite to anyone with multiple sclerosis,” Jennifer Powell, a California resident living with secondary progressive MS since 2009, wrote in a Multiple Sclerosis News Today column.
Heat intolerance in MS can manifest in a number of ways, and symptoms may range from unpleasant to debilitating. Patients often report increases in fatigue, weakness, vision problems, as well as trouble moving around and difficulty thinking.
“As my cognition slows, so do my motor movements. My foot drop becomes more pronounced as I stumble into the kitchen for more gel packs,” Powell wrote, describing her experience with heat sensitivity. “I begin to grow fatigued and recall the symptoms associated with heat stroke. I drag my lethargic self into a cool shower.”
The phenomenon of worsening symptoms during heat exposure is sometimes called a pseudo-exacerbation, as it may feel like an MS relapse. These pseudo-relapses, however, are not caused by an increase in disease activity and are shown to resolve when the person cools down.
“I relished in the warm summer days,” Powell wrote in another Multiple Sclerosis News Today column. Now, “I dread the season I used to find fun, adventurous, and alluring, instead opting for the cool and controlled climate in my home.”
Common MS symptoms that worsen with heat
Some of the common MS symptoms that worsen with heat include:
- fatigue
- cognitive challenges
- numbness, tingling, or other unusual sensations (dysesthesias)
- tremor
- weakness or coordination problems
- blurry vision
How to deal with heat intolerance in MS
It’s generally recommended that MS patients who experience heat sensitivity or heat sensation should take steps to stay cool to prevent unpleasant symptom worsening. Common strategies and tips to ease the effects of heat include:
- wearing cooling clothing or linens
- using equipment including fans, air conditioners, or air coolers
- staying hydrated, regularly drinking cold drinks, or sucking on ice or frozen fruit
- spritzing the face and wrists with cold water
- taking care when bathing to start with tepid water
- avoiding places that are especially hot, humid, or crowded
- picking cooler times of day for exercising outside, usually early morning or evening, particularly during summer heat or a heat wave
- taking a cold shower to reduce core body temperature following activity or exposure to a hot environment
- eating lighter meals, such as salads, or a cool dessert
Does cold make MS symptoms worse?
Though less common than sensitivity to heat, some people with MS report some symptoms worsen in response to cold temperatures. Cold sensitivity is usually managed by taking steps to stay warm, such as layering clothing or using a heater.
Cold sensitivity tends to affect different symptoms than heat sensitivity. Common symptoms that worsen due to cold may include:
- spasms and spasticity, or abnormally tight muscles
- mobility problems
- nerve pain
- depression
- fatigue
MS history: the hot bath test
Before modern medical technologies such as MRI scans, testing for heat intolerance was one of the main ways doctors would diagnose MS. The hot bath test, or hot water test, as its name implies, simply involved having patients with suspected MS submerge themselves in a bath of hot water, and then waiting to see if their symptoms got worse in response to the heat.
Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
FAQs about heat intolerance and MS
No. Exposure to extreme heat can result in a temporary worsening of multiple sclerosis (MS) symptoms, but this phenomenon is different from a true relapse. MS relapses are caused by increases in disease activity that last for at least 24 hours. In contrast, the pseudo-exacerbations that occur due to temperature sensitivity are not caused by disease progression and resolve after body temperature is restored.
Sunlight exposure is associated with a lower risk of developing multiple sclerosis and has also been shown to reduce disease severity in people with the condition. This protective effect is believed to be mainly mediated by vitamin D, which is produced in the skin upon exposure to sunlight and is important for modulating immune system activity. However, MS patients with heat sensitivity, and those whose symptoms and medications may increase sun sensitivity, should avoid sunbathing and direct exposure to sunlight, particularly during periods of hot weather and high humidity.
Hot water showers and baths are sources of heat that can result in elevations in core body temperature. In multiple sclerosis (MS) patients, this can further interfere with electrical signals from already damaged nerves and lead to a temporary exacerbation of symptoms or the appearance of new ones. However, if patients can tolerate the heat well, hot tubs may be a good approach to ease MS symptoms such as muscle stiffness and nerve pain. It is generally recommended patients ask their healthcare team if hot tubs are safe in their situation.
The abnormal immune response that drives multiple sclerosis (MS) can cause damage to brain regions involved in regulating body temperature. Indeed, several studies have shown people with MS have an impaired sweating response, manifesting as delayed or reduced sweating in response to heat, which makes it difficult for them to maintain normal temperatures. This also may contribute to heat sensitivity in MS.
While many people with multiple sclerosis (MS) have a reduced sweating response, there are several reports of patients who experience severe bouts of hot flashes and night sweats. This may be associated with MS-related damage in the autonomic nervous system, which helps control involuntary bodily processes like sweating. It also can be a side effect of certain MS treatments.
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