Heat intolerance is also called hypersensitivity to heat. Symptoms may include headache, dizziness, weakness, cramping, or nausea. This usually happens because your body isn’t regulating its temperature properly.

Most people don’t like extreme heat, but you might find that you’re always uncomfortable in hot weather if you have heat intolerance.

The hypothalamus is a part of the brain that regulates your body’s temperature. When you get too hot, your hypothalamus signals through your nerves to your skin to increase sweat production. When sweat evaporates off your skin, it cools your body down.

This is how your body regulates and maintains a delicate balance between hot and cold. Sometimes, you can have a stronger reaction to heat, presenting as excessive sweating, fatigue, dizziness, dehydration, and malaise. This can be a sign of heat intolerance.

Heat intolerance is not a medical condition in itself. It can indicate a variety of things. Read on to learn what causes heat intolerance and what to do about it.

Heat intolerance has a variety of potential causes.


One of the most common causes of heat intolerance is medication. Medications that can affect how your body regulates heat include:

These medications work in different ways but can inhibit your body’s ability to cool by inhibiting sweat production.


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.

Excessing this hormone can cause your body’s metabolism to increase, raising your 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 usual.

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.

Learn more about heat exhaustion vs. heat stroke.

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.

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.

Heat intolerance or heat hypersensitivity occurs when you experience excessive sweating and discomfort as your body tries to cool down when exposed to heat.

Many things can cause heat intolerance, from conditions like MS to certain medications. If you are experiencing heat intolerance, speak with your doctor to find the cause and the best treatment.