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Heat Intolerance

Most people do not like extreme heat, but you might find that it is impossible for you to be comfortable in hot weather if you have heat intolerance. Heat intolerance is also referred to as hypersensitivity to heat.

When you suffer from heat intolerance, it is often because your body is not regulating its temperature properly. Your body regulates its temperature by maintaining a delicate balance between hot and cold. The hypothalamus is a part of the brain that regulates your body’s temperature. When you get too hot, your hypothalamus sends a signal through your nerves to your skin, telling it to increase sweat production. When sweat evaporates off of your skin, it cools your body down.

What Leads to Heat Intolerance? 

Heat intolerance has a variety of potential causes.


One of the most common causes of sensitivity to heat is medication. Allergy, blood pressure, and decongestant medications are among the most common. Allergy medications can inhibit your body’s ability to cool itself by preventing sweating. Blood pressure medications and decongestants may decrease the blood flow to your skin. This also inhibits sweat production. Decongestants can cause increased muscle activity, which can raise your body’s temperature.


Caffeine is a stimulant that can increase heart rate and speed up metabolism. This can cause your body temperature to rise and lead to heat intolerance.


Hyperthyroidism occurs when your thyroid produces too much of the hormone thyroxine. Thyroxine affects the regulation of your body’s metabolism. An excess of this hormone can cause your body’s metabolism to increase, which leads to a rising body temperature. Graves’ disease is the most common cause of hyperthyroidism. Graves’ disease is an autoimmune disorder. In this disease, the immune system produces antibodies that make the thyroid produce too much thyroid hormone.

Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a debilitating disease that affects your central nervous system. The central nervous system is made up of your brain and spinal cord. This disease affects the protective covering, or myelin, of the nerves of your central nervous system. If your myelin is damaged, your body’s nerve signals become interrupted. This condition can lead to heat intolerance.

What Are Some Signs I Should Look Out For?

Being heat intolerant can make you feel as though you are overheating. Heavy sweating is also extremely common in those that suffer from heat intolerance. The symptoms may occur gradually, but once the intolerance develops, it usually lasts for a day or two. Other potential signs of sensitivity to heat include:

  • headache
  • dizziness
  • weakness
  • cramping
  • nausea

Having a temperature between 100.4ºF and 104.9ºF when you are not otherwise ill can also signal that you are sensitive to heat. Your heartbeat might also be faster than normal.

Potential Complications of Heat Intolerance

If you have MS, heat intolerance can lead to vision problems. This can range from blurred vision to temporary loss of vision. A rise in body temperature amplifies the distortion of nerve signals in those with MS. This is referred to as Uhthoff’s phenomenon, which is named after Wilhelm Uhthoff who discovered the connection between heat and vision problems. This worsening of symptoms is only temporary and is usually resolved by cooling off.

Heat intolerance may lead to heat exhaustion under severe circumstances. Symptoms of heat exhaustion include:

  • confusion
  • loss of consciousness
  • vomiting
  • muscle cramps
  • body temperature of 104ºF or higher
  • elevated heart rate
  • rapid breathing

If you experience these symptoms in addition to heat intolerance, seek medical attention immediately. Heat exhaustion can lead to heatstroke if it is left untreated. This can be fatal.

Treating and Preventing Your Symptoms

There are things you can do to protect yourself from feeling the effects of heat sensitivity. Staying in a cooled environment is one of the best ways to avoid the symptoms. If you live somewhere without air conditioning and you have MS, you may be able to deduct the cost of your fans and cooling equipment as a medical expense. This is usually only possible if your doctor has written you a prescription for it.

You should also drink plenty of water to keep yourself hydrated. Sweating too much can quickly dehydrate you. You might also try drinking iced drinks. Wearing lightweight cotton fabrics will allow the air to reach your skin and cool you. If you play sports, only wear extra protective gear like gloves, armbands, and hats when necessary.

Content licensed from:

Written by: Carmella Wint
Medically reviewed on: Sep 15, 2015: Steven Kim, MD

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