Thermoregulation – what is it?

Thermoregulation is the process where our body and brain maintains our core (internal) temperature when we are exposed to rises or falls in the temperature of our environment or increased physical activity.  It is estimated that heat sensitivity is experienced in 60- 80% of those diagnosed with MS. Many individuals with heat sensitivity experience a temporary worsening of clinical signs and neurological symptoms when exposed to heat. This can also occur with exposure to high humidity levels.

Though less studied than heat sensitivity, when exposed to cold temperatures, many individuals with MS experience an increase in symptoms and changes in function as well.  In both cases, these changes are usually reversed quickly by taking action to return the body temperature to normal levels.  For example, if you are overheated, go inside to an air-conditioned space, take a cool shower, or drink a glass of ice water. All of these measures have been shown to help return your body temperature back to normal.

Alternatively, if your body is very cold, you can go inside where it is warm, drink a warm beverage, or put on more clothing layers to help warm your body back to a normal state.


How Temperature Changes Affect Your MS

Tolerating the high temperatures over summer months and low temperatures during winter months is a challenge for many living with MS.  Although these changes are often considered temporary and not believed to damage nerves or worsen MS, there are published reports of intense or prolonged exposures leading to a MS relapse or attack. We know that attacks have the potential to damage nerves.  You can take measures to reduce the impact of temperature changes and enjoy life safely and comfortably in all seasons!

So, what causes our body temperature to change?

Many things can raise the body’s temperature, such as being outdoors in a hot or humid climate, hot showers or baths, exercise, digestion, and illnesses or infections (which often will cause a fever).  In colder climates, a reduction in temperature occurs with exposure to lower temperatures such as occurs in winter months.

The most comfortable, healthy and safe temperature for the human body is between 98oF(37oC) and 100oF (37.8o (C).  Normally, the human body is able to maintain a safe temperature through a process called thermoregulation.  

When the body temperature rises, signals are sent to the brain, which responds and sends signals to the body in an effort to return the core body temperature to a safer level.  Measures such as sweating and vasodilation (increasing the blood flow at the skin surface) cool down the body when overheating occurs.

When the body temperature falls, skin cold receptors take notice, and send signals to the temperature regulation centers of the brain.  The brain’s response is to direct the body to tighten blood vessels in the skin to maintain warmth and boost other efforts to conserve heat, like shivering and rerouting blood flow.


How Does MS Affect Your Temperature Regulation?

In MS, the body systems designed to self regulate may be either ineffective or in some cases, may not work at all if MS lesions have damaged those areas of the brain.   In addition, any damaged nerves may have difficulty sending and receiving the messages from the brain when exposed to the temperature changes.  When this happens, you may notice symptoms arising that you have previously experienced and in some case, new symptoms may occur.

Although not completely understood, it is believed that the cause of this sensitivity to heat and/or cold is a combination of factors:

1) The damage that occurs to the nerves of the brain and spinal cord through the demyelination process may impact the nerve signaling or conduction.  In this case, normal nerve conduction is slowed or absent when body temperatures change.  In this case the functions controlled by the damaged nerves are altered and you may experience changes in function such as changes in vision, slowing of movements, and sensory changes such as numbness and tingling.  In addition, signals from your body that normally carry messages to the brain that you are getting hot or cold may not getting through.  It could also mean that the brain receives the messages that you are hot/cold, but the damage nerves do not carry the signals from the brain to the body to tell it what to do in response.

2) Depending on where the MS damage is in brain, your body may be sending the signals that you are hot or cold but your brain may have difficulty interpreting these signals. It would be like receiving an urgent text message in a foreign language that you do not understand.  You can see the message, but have no idea what it means or how to respond. The end result is that your brain’s difficulty interpreting the signals means that you may not be aware that your body has experienced a significant temperature change. This places those with MS at a higher risk to experience problems when their body temperatures are elevated or decreased.


What if your body cools off / heats up just fine, but you are still experiencing symptoms with these temperature changes?

The reason for this is that sometimes, the nerves themselves are irritated with these fluctuations in body temperature. Damaged nerves tend to be even more irritated. This can lead to symptoms of MS being experienced such as temporary limb numbness, vision changes, vertigo, fatigue, etc.  For some, even a 0.5 o C or 1 o F increase or decrease in body temperature can bring on MS symptoms, while others may not experience symptoms until more extreme changes occur.

A term often used by healthcare professionals to describe these temporary changes in MS symptoms is pseudo-relapse.  These short-term fluctuations in symptoms often disappear once the stressor (heat or cold exposure) is removed or the body is cooled / warmed back to a normal temperature.

There are also people with MS who are not impacted by temperature changes at all and in fact, report experiencing an increase in function and reduction of symptoms with temperature changes.




  • Fatigue is one of the most common symptoms experienced with changes in body temperatures.  Studies show that this may be a feeling of general fatigue (feelings of being tired and lack of energy) and / or direct muscle weakness of major muscles. Some people experience weakness in this case.
  • Cognitive function may worsen with heat exposure.  These symptoms include changes in memory, how quick you can process your thoughts, your ability to multitask, and a general feeling some refer to a foggy thinking.
  • Sensory symptoms are commonly reported with heat exposure.  These may include numbness, tingling, pain or other sensations that you do not normally feel, or a worsening of those you have experienced with MS previously.
  • Eyes and vision symptoms are especially concerning with heat exposure.  This can include blurry or double vision, and sometimes unexpected eye movements that you have no control over. This can be a major problem when driving!
  • Bladder control can become a problem with heat exposure for those with difficulties maintaining bladder control.
  • With MS, most any symptom could arise or worsen in those with heat or cold sensitivity when exposed to changes in temperature.

Symptoms commonly reported by those with cold sensitivity often include increased spasticity and stiffness in their arms and legs or changes in normal function or mobility, such as walking and moving around freely.  There have even been reports of people experiencing changes in symptoms when cool air is blowing directly onto their arms / legs such as with fans or air vents.




If you experience symptoms or changes in function with exposure to heat or cold, take measures to return your body to a normal temperature (cooling or warming the body).  If however, your symptoms continue to worsen despite returning to a normal temperature, or if they last longer than 24 hours, notify your physician to be evaluated immediately.

Please see our “Tips for regulating your body temperature” here (insert link to Tips) and let us point your compass in the right direction.




Berger, JR. & Sheremata, WA (1983).  Persistent Neurological Deficit Precipitated by Hot Bath Test in Multiple SclerosisJAMA 249(13): 1751-1753.

Davis, Scott L., Wilson, Thad E., White, Andrea T., & Frohman, Elliot M. (2010). Thermoregulation in Multiple Sclerosis. J Appl Physiol: 109(5): 1531 – 1537.

Huitinga, I, De Groot, CJ, Van der Valk, P, Kamphorst, W, Tilders, FJ, Swabb, DF (2001 Dec).  Hypothalamic Lesions in Multiple Sclerosis. J Neuropathol Exp Neurol; 60(12): 1208-18.

White, KD, Scoones, DJ & Newman, PK (1996).  Hypothermia in Multiple Sclerosis. J Neurol Neurosurg Psychiatry: Oct 61(4) 369-375.

Multiple Sclerosis Association of America (MSAA) Cooling and Assistive Equipment Program offers financial support for adults and children with MS who are heat sensitive.

National Multiple Sclerosis Society (NMSS):  Heat and Temperature Sensitivity.