Heat intolerance or temperature regulation disorder

"The thermostat that is broken"


Temperature dysregulation is a fairly common complaint after brain injury. These complaints can also occur with other conditions that are not related to brain injury, which is why it is important to be able to prove a brain injury.
In the event of temperature dysregulation, the body thermostat simply does not function properly. A person cannot warm up sufficiently in cold weather and, conversely, cannot cool down in warm temperatures. The brainstem, the hypothalamus, the hair, skin and the unmyelinated nerve pathways play a major role in this.


With heat:
The body automatically regulates that sweat glands in the skin release more sweat. The sweat evaporates and allows heat energy to be removed from the skin.
Blood vessels leading to the capillaries dilate, allowing more blood to flow through the skin and more heat to be removed. The hairs on the skin lie flat in warm weather.


In cold:
The body automatically regulates muscles to contract quickly - shivering. Shivering requires energy from breathing, and some of this is released as heat.
Blood vessels leading to the capillaries of the skin narrow, causing less blood to flow through the skin and
heat can be retained in the body. The hairs trap a layer of air above the skin, which helps to insulate the skin against heat loss.
The hypothalamus activates the muscles of the hair to straighten. Goosebumps arise. The hair then 'stands up'.
If this no longer happens automatically, dysregulation can occur. We explain this on this page. We also mention the symptoms of heat stroke and the various conditions that cause heat intolerance.


Have complaints or feel ill on hot days

Although many people enjoy when the sun shines brightly and temperatures rise, there are people with brain injuries and other neurological disorders who dread these days. They can experience limiting problems in heat or on warmer days or literally become ill.
We increasingly hear the opposite: people who become unwell in the cold and are then unable to warm up.


Whch people suffer from the heat?

Everyone can feel tired, dull and lifeless when the weather is too hot, but specifically people with a spinal cord injury above the fifth thoracic vertebra and people with brain damage can become unwell on hot days. This can also be done during a sauna visit or during a warm bath. Older people who are less able to perspire or children whose bodies cannot yet lose heat properly can also become ill from hot weather.
People who use certain medications such as blood pressure medication or thyroid medication may become less tolerant to heat. Overweight people, whose blood circulation is already strained, use more energy and feel hot more quickly. People with Dysautonomia/POTS or another physical disability can also quickly develop complaints.



The hypothalamus is responsible for regulating body temperature. It regulates the correct temperature in hot or cold conditions. It receives information from temperature-sensitive receptors in the skin and circulation. The hypothalamus then sends signals to the body to sweat when it gets too hot, or to develop goosebumps to retain heat, or to shiver when it gets cold.
At high temperatures, the nerve fibers are less able to transmit signals to and from the brain. This is particularly a well-known phenomenon in MS, Multiple Sclerosis.


Because the blood thickens and becomes more viscous at high temperatures, the risk of thrombosis also increases. Thrombosis means that a blood vessel becomes blocked by a blood clot. This can be in the deep veins, such as with a thrombosed leg, but a clot can also break loose and end up in the lungs (pulmonary embolism), intestines (intestinal infarction) or in the brain (cerebral infarction). It is therefore advisable to keep moving on hot days. If you have no choice but to sit or lie down, try moving your leg every 15 minutes; Bend and stretch your toes 30 times, rotate your feet in circles.
It is also important to take in plenty of fluids.



The brainstem controls and regulates the autonomic nervous system: breathing, heart rate, blood pressure and circulation, reflexes of vision and hearing (startle response), sweating, digestion, body temperature, pupil size.
Especially in warm weather, sweat function, blood circulation and body temperature are so important. Damage to the brainstem therefore has many residual consequences. Temperature dysregulation is one of them, but it does not occur in all brainstem injuries. This means that the body can no longer warm itself at low temperatures.


Complaints of heat dysregulation in case of neurological disorders

Complaints may include:

  • weakness
  • fatigue
    • complaints of fatigue or exhaustion can be amplified
  • problems in cognition (thinking, concentration and attention, planning, keeping an overview)
    • overstimulation can increase
  • emotional change
  • being down because the person is extra confronted with the limitations and vulnerability during hot days
  • problems with balance
  • temporary worsening of neurological complaints
  • vision problems
    • blurred vision leading to temporary loss of vision
  • dizzy, headache, muscle pain
  • complaints similar to sunstroke - see paragraph below
  • feeling unwell, unconsciousness
  • a disturbance in the regulation of body temperature can occur due to changes in the nervous system. In that case, a person may be too cold or feel too hot with a body temperature around 38°C. A person may even have a fever and wake up during the night, drenched in sweat.


Sunstroke, affected by heat, heat stroke

Dehydration of the body in particular leads to 'heat stroke'. Caused by perspiration or drinking too little. The term 'sunstroke' is dubious and confusing for the different stages of heat-sickness. Heat stroke, the final stage, can be fatal.



  • heat cramps: abdominal pain, muscle cramps
  • heat engorgement: headache, nausea, red head
  • heat stroke / heat exhaustion; confusion, delirium, unconsciousness, vomiting, gray clammy skin, seizures, muscle cramps, body temperature of 40 °C or higher, accelerated heart rate, rapid breathing, shock, cardiac death.

If you have signs or see someone with signs of heat exhaustion or heat stroke, cool down immediately and seek emergency medical attention.

  • confusion
  • delirium
  • loss of consciousness, fainting
  • vomiting
  • muscle cramps
  • body temperature of 40°C or higher
  • increased heartrate
  • rapid breathing
  • go into shock

If your body becomes warmer than 42 °C, it is life-threatening. The proteins in the body coagulate around that temperature. This also applies to the proteins that regulate your body temperature. They then no longer function.


General measures

  • Wear lightweight clothing to allow the skin to cool.
  • Avoid sun on the head and body.
  • Find a cool and quiet shady spot.
  • Try to keep the sun away from windows.
  • Keep doors and windows closed to the warm outside air during the day. This prevents too warm air from flowing in. Only open them when the temperature cools in the evening.
  • Drink enough water.
  • Cool with fan, air conditioning, wet towels, cooling vest, see for example here
  • Prepare a cool foot bath.
  • Stop activities that are strenuous.
  • The chance of a salt deficiency is very small, even with warm temperatures. Make sure you have salty food at home, such as nuts, licorice, salted herring, stock or saline solution.
  • In case of heat exhaustion without unconsciousness: drink plenty of fluids; saline solutions or sports drinks, avoid cold drinks! Cold drinks cause the skin vessels to narrow so that heat can no longer escape.
  • In case of heat exhaustion with unconsciousness: do not drink but cool! Call a doctor.
  • Make an emergency plan in advance for what to do in case of heat. People with brain damage are less able to think and act well in heat. Be prepared. Have the phone ready with the ICE numbers.
  • Realize that you can be less taxing and have to find a new balance between activities and rest during heat days. Prepare for it and keep in mind that it is temporary, otherwise you can suffer a lot mentally during a heat wave.


Temporary worsening of neurological complaints: Uthoff's sign / phenomenon

An increase in body temperature increases the distortion of the body's nerve signals in people with MS, among others. This is called Uhthoff's sign or phenomenon, after Wilhelm Uhthoff who discovered a link between heat and vision problems, such as blurred vision to temporary vision loss.
The symptoms get worse temporarily and disappear when the body cools down.
The phenomenon can occur with any neurological disorder that causes demyelination, such as MLD/leucodystrophy, acute disseminated encephalomyelitis, TSP, but it also occurs with normal aging.


Inability to warm up at low temperatures

Freezing cold also does something to the head. We hear a lot from people that they have become unwell in cold weather. The brain stem and the tiny blood vessels in the nerve pathways also play a role in this. Life can become very limited if you cannot participate in public life because of the outside temperature that is completely normal for others.


Other conditions involving heat intolerance




Breitner S, Wolf K, Peters A, et al (June 6, 2014)

Short-term effects of air temperature on cause-specific cardiovascular mortality in Bavaria, Germany Heart 2014;100:1272-1280.



Damnjanović Z, Jovanović M, Bogdanović D, Smiljković I, Ilić N, Damnjanović I. Relationship between the incidence of idiopathic lower extremity deep vein thrombosis and the location of the thrombus depending on the changes of atmospheric pressure. Chirurgia (Bucur) 2012;107:483–487. [PubMed] Esquenet APD, Boudet J, Sevestre-Pietri MA, Ganry O, Pietri J. [Effect of meteorological variations on the emergence of deep venous thrombosis of the leg] J Mal Vasc. 1997;22:244–248. [PubMed] Ladenson Kim M, P. Thyroid. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 233.

Winkenwerder W Jr., Sawka MN. Disorders due to heat and cold. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 109.


prof. dr. Jan M. KeppelHesselink; http://www.neuropathie.nu/diagnose/zenuwfunctie-enzenuwvezeldikte.html , http://www.ad.nl/ad/nl/4560/Gezond/article/detail/2321514/2006/07/25/Letterlijk-ziek-van-de-hitte.dhtml


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