Most people don’t like extreme heat, but you might find that you’re always uncomfortable in hot weather if you have heat intolerance. Heat intolerance is also referred to as hypersensitivity to heat.

When you have heat intolerance, it’s often because your body isn’t 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.

Heat intolerance has a variety of potential causes.


One of the most common causes of heat intolerance 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 your heart rate and speed up your 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. It’s an autoimmune disorder that causes the thyroid gland to produce too much thyroid hormone.

Multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system. The central nervous system is made up of the 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.

Being heat intolerant can make you feel as though you’re overheating. Heavy sweating is also very common in people who have 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:

Your heartbeat might also be faster than normal.

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 people with MS. This is referred to as Uhthoff’s phenomenon. This worsening of symptoms is only temporary. It’s 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 (40ºC) 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 left untreated. This can be fatal.

Here are some ways to protect yourself from feeling the effects of heat sensitivity:

  • Stay in a cooled environment. This is one of the best ways to avoid the symptoms.
  • Drink plenty of water or iced drinks to keep yourself hydrated. Sweating too much can quickly dehydrate you.
  • Wear lightweight cotton fabrics. They 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.

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.

If you have heat intolerance due to hyperthyroidism, speak with your doctor about treatment options that may help reduce your sensitivity. Depending on the severity of your condition, this may include medications, radioactive iodine, or surgery.