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Heat Sensitivity in Multiple Sclerosis

It is estimated that 60-80% of those living with MS experience ‘heat sensitivity’.  This show up as a transient and temporary worsening of neurological symptoms when their body temperature is elevated. These changes are usually reversed quickly by removing the heat stressor and cooling the body.  Tolerating the rising temperatures over summer months is a challenge for many (especially here in Texas!).  Many factors can have an affect on the body’s temperature such as being outdoors having ‘fun in the sun’, hot baths or showers, exercise, sunbathing, enjoying hot tubs, and illness or infection, which often will bring about a fever.

Normally, the human body is able to maintain a tolerable internal or core temperature through a process called thermoregulation.  When the body temperature rises, automatic measures such as sweating and vasodilatation (increasing the blood flow at the skin surface) begin to cool down the body.   Unfortunately, in MS these measures are either ineffective or not occurring at all due to the nerve damage caused by the disease.  Although not completely understood, it is believed that the cause of this sensitivity to heat 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 conduction.  In this case, the normal responses are slowed or absent when body temperatures rise.

2)    In MS there may also be impairment of thermoregulation systems of the body directly and indirectly through the disease process itself.  In those who experience this type of damage, the ability to reduce temperatures through sweating and vasodilatation may be impaired.

The end result is the inability of the body to regulate the internal temperature combined with damage to nerves from the MS which results in a slowing of nerve conduction. 

*This places those with MS at a higher risk to experience problems when their body temperatures are elevated. 


Symptoms experienced by those with heat sensitivity with MS vary both is type and severity.  For some, even slight increases can bring on symptoms while others may not experience symptoms until there is more of pronounced increases noted.  There are individuals with MS who actually experience improvement in symptoms with heat exposure.

·      Fatigue is one of the most common symptoms experienced with rising body temperatures.  Studies show that this may be an experience general fatigue (feelings of being tired and lack of energy) and / or direct muscle weakness of major muscles.

·      Cognitive function may worsen with heat exposure.  These symptoms include changes in memory, processing speeds of your thoughts, being able to multitask and a general feeling some refer to a ‘foggy’ thinking.

·      Sensory symptoms have been 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 normally experience with MS.

·      Eyes and vision symptoms are especially concerning with heat exposure.  This can include blurry vision and sometimes unexpected eye movements that you have no control over.

·      Bladder control can become a problem with heat exposure for those with bladder involvement. 

·      Most any previously experienced symptoms can resurface during times of heat exposure in those who are sensitive to elevations in temperature.


A term often used by healthcare professionals to describe these temporary changes in symptoms is “pseudo-relapse”.  These temporary fluctuations in symptoms often disappear once the body is cooled back to a normal temperature.  If however, your symptoms continue to worsen despite cooling off or if they last longer than 24-48 hours, notify your physician so that you can be evaluated immediately.


The goal is to be an active participant in life throughout the year regardless of environmental temperature.  It is important to find ways to stay healthy and active while being aware of your level of heat sensitivity and taking precautions to minimize the impact. 

·      A great way to identify your particular symptoms and temperature tolerance is to track your response to various levels of temperature changes.  More often than not, the symptoms will come on gradually and individuals with heat sensitivity can identify subtle changes early to be able to cool off and avoid more severe changes that can not only be frustrating but can also place you in extreme danger. 

·      Combine a little bit of attention to your body temperature with a touch of creativity and you will be able to enjoy the summer months safely!

Look for the next section on tips for dealing with heat sensitivity!

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