Heat intolerance is an unusual sensitivity to heat. People with heat intolerance may feel hot when others feel comfortable or even cold.
They may also have an unusual response to heat, such as intense sweating or anxiety. Heat intolerance is not a disease, but it can be a symptom of an underlying medical condition.
In this article, learn about the causes of heat intolerance, how to manage it, and when to see a doctor.
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
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:
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.
People with heat intolerance should discuss their symptoms with a doctor, especially if the symptoms appear suddenly or get progressively worse.
To treat heat intolerance, doctors will focus on treating any underlying medical conditions. Treatment will vary widely depending on the underlying condition. For example, people with Graves' disease may need radioiodine therapy to restore normal thyroid levels.
In many cases, heat intolerance is not fully preventable or treatable. A person with a spinal cord injury may have difficulty in extreme heat no matter what treatment they choose.
People may find that avoiding heat where possible and adopting strategies for safely managing any necessary time in hot conditions will help in the long term. 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:
- a rapid pulse
- very heavy sweating
- muscle cramps
- a headache
- extreme fatigue or fainting
- changes in mood
Seek immediate medical attention for:
- an inability to sweat, even when very warm
- a body temperature above 103°F
- loss of consciousness
Managing medical conditions that cause heat intolerance can help prevent symptoms.
Talk to a doctor about staying safe in the heat and ask whether any medications are available to help the body regulate its temperature.
Some strategies that can reduce the risk of heat intolerance include:
- Maintaining a healthy body weight. Heavier people may have more difficulty cooling their bodies.
- Getting plenty of exercise to remain physically fit. People with good heart and lung health tend to respond better to the heat.
- Limiting or avoiding alcohol and drug use. Excessive alcohol consumption and the abuse of some drugs, such as amphetamines, may increase heat sensitivity.
- Keeping blood sugar levels in check. People with diabetes may be more vulnerable to the heat, especially when their blood sugar levels are too low or too high.
- Drinking plenty of water. Extreme heat saps the body of water through sweating. If the body cannot sweat, it cannot stay cool, so staying hydrated is critical.
As many people enjoy outdoor activities, such as swimming and warm-weather festivities, those with heat intolerance may feel frustrated and excluded. However, the right treatment strategy and a few cooling measures may make the heat feel more manageable.
Heat intolerance can provide clues to a person's overall health. It suggests that either the body may not be able to cool itself down properly, the brain may not be responding correctly to heat, or the heart and lungs may be struggling to work efficiently enough.
Anyone experiencing new or worsening heat intolerance should speak to a doctor, who can help diagnose the underlying problem.