Heat intolerance
A symptom of feeling overheated with excessive sweating.
Wikipedia / Wikimedia Commons
Heat intolerance is a condition where a person feels uncomfortably hot and sweats heavily, even in mildly warm surroundings or when the temperature rises. Unlike heatstroke or other heat-related illnesses, it is not typically caused by exercise or hot, humid weather. Instead, it usually signals an underlying issue, such as an endocrine disorder, a side effect of medication, or another medical condition.
Symptoms include a subjective feeling of being overheated and sweating that may be excessive. In people with multiple sclerosis, heat intolerance can trigger a pseudoexacerbation—a temporary worsening of MS symptoms. Similarly, those with postural orthostatic tachycardia syndrome (POTS) or dysautonomia may experience a temporary flare-up of their symptoms.
Diagnosis relies mainly on a patient’s history, followed by blood tests and other exams to identify the root cause. In women, hot flashes must be ruled out.
The most common cause is an excess of thyroid hormone, known as thyrotoxicosis (as in hyperthyroidism). Other causes include stimulants (e.g., amphetamines, caffeine, appetite suppressants), anticholinergics and drugs that impair sweating, malignant hyperthermia susceptibility, menopause, multiple sclerosis, fibromyalgia, diabetes, hypothalamic tumors, methadone treatment, dysautonomia, POTS, sensory defensiveness or sensory processing disorder, and serotonin syndrome.
Treatment focuses on making the person more comfortable and, if possible, addressing the underlying cause. Staying in a cool environment and drinking extra fluids—especially if sweating is heavy—can help. Cooling vests may be used preventively to lower body temperature or to relieve symptoms when they occur.
- Field
- Medicine
- Symptom type
- Heat-related symptom
- Common cause
- Excess thyroid hormone (thyrotoxicosis)
- Associated conditions
- Multiple sclerosis, POTS, dysautonomia, menopause, fibromyalgia, diabetes
- Diagnosis method
- Patient history, blood tests, other medical tests
Lore & Background
Heat intolerance is a symptom that manifests as a subjective feeling of being overheated, often accompanied by excessive sweating, when the ambient temperature rises. It is distinct from heat illnesses such as heatstroke, as it typically stems from underlying medical conditions or drug effects rather than environmental exposure alone. The most common cause is excess thyroid hormone, known as thyrotoxicosis, which can occur in hyperthyroidism.
Reader's Guide
Heat intolerance serves as a clinical marker for various endocrine, neurological, and pharmacological conditions. Its diagnosis relies heavily on patient history, followed by blood tests to identify underlying causes such as hyperthyroidism, menopause, or multiple sclerosis. In patients with multiple sclerosis, heat intolerance can trigger a pseudoexacerbation—a temporary worsening of MS symptoms. Similarly, those with postural orthostatic tachycardia syndrome (POTS) or dysautonomia may experience temporary symptom worsening. Treatment focuses on comfort and addressing the root cause, with strategies including staying in cool environments, increasing fluid intake, and using cooling vests. The symptom's broad association with conditions like fibromyalgia, diabetes, and serotonin syndrome underscores its importance as a diagnostic clue in clinical practice.
Did You Know?
- Heat intolerance is usually a symptom of endocrine disorders, drugs, or other medical conditions, not heatstroke.
- Excess thyroid hormone (thyrotoxicosis) is the most common cause of heat intolerance.
- In multiple sclerosis, heat intolerance may cause a temporary worsening of MS-related symptoms called a pseudoexacerbation.
- Cooling vests can be used as a preventative tool to reduce body temperature or when symptoms present.
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