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Heat intolerance is when someone feels too warm in temperatures that other people find comfortable. It can be a mild discomfort or significantly affect a person’s quality of life. Heat intolerance is a generic symptom that can refer to a wide variety of responses to heat.
Some people with heat intolerance merely dislike the heat. Others feel uncomfortably hot at temperatures that other people find comfortable. Some people can develop serious or even life-threatening symptoms in response to heat. According to the Centers for Disease Control and Protection (CDC), heat-related illnesses, such as heat stroke, are responsible for more than 600 deaths in the United States each year.
People with heat intolerance need to be cautious in extreme heat, especially when they have other risk factors for heat-related illnesses. The symptoms of heat intolerance can vary from person to person but may include:
- feeling very hot in moderately warm temperatures
- excessive sweating
- not sweating enough in the heat
- exhaustion and fatigue during warm weather
- nausea, vomiting, or dizziness in response to heat
- changes in mood when too hot
People with certain chronic illnesses, such as multiple sclerosis (MS), may find that their symptoms temporarily worsen in the heat. Some people with heat intolerance are also cold intolerant.
Those with heat intolerance may have a disorder called dysautonomia that affects their autonomic nervous system. The autonomic nervous system helps regulate automatic functions of the body, including the body’s response to heat.
Several medical conditions can cause dysautonomia, including: diabetes, alcohol use disorder, Parkinson’s disease, Guillain-Barré syndrome and mitochondrial disease. Other causes of heat intolerance include:
Age
Infants, children under 4 years old, and older adults may be more sensitive to the heat. This sensitivity increases their susceptibility to heat-related illnesses, such as heat stroke.
Medication
Some medications change the body’s response to heat, for example, by decreasing sweat production. Anticholinergic drugs, which can treat many psychiatric conditions and Parkinson’s disease, may reduce sweating and increase heat sensitivity.
Sensory issues
Sensory processing disorder, as well as sensory issues that sometimes accompany autism, may make a person more sensitive to heat.
Neurological conditions
Medical conditions that affect the brain and spinal cord, such as spinal cord injuries and MS, can increase heat sensitivity by changing how the body or brain processes heat or by inhibiting the body’s ability to regulate temperature.
Endocrine system problems
The endocrine system helps the body regulate a wide range of functions. Disorders such as Graves’ disease, a thyroid condition, can increase heat sensitivity.
Being less physically fit
For some people, heat intolerance is a sign of poor cardiovascular and respiratory fitness. In 2014, researchers found that people who showed more signs of heat intolerance were also less physically fit.
Ways to manage heat intolerance include:
Avoiding direct sunlight.
The sun tends to be at its hottest and brightest between 11 a.m. and 3 p.m. Using air conditioning or a fan during the summer months.
Drinking plenty of fluids to avoid dehydration.
Wearing light-colored, loose-fitting clothing.
Avoiding alcohol in hot weather.
Taking a cool bath or swimming in a pool.
Wrapping a towel soaked in cold water around the back of the neck.
Avoiding strenuous activities during hot weather or in warm rooms.
People with heat intolerance should carefully monitor themselves for signs of heat-related illness, such as: nausea, dizziness, vomiting, a rapid pulse, very heavy sweating, muscle cramps, a headache, extreme fatigue or fainting and changes in mood.
Seek immediate medical attention for:
an inability to sweat, even when very warm
a body temperature above 103°F
confusion
loss of consciousness