Heat intolerance is a symptom reported by people who feel uncomfortable in hot environments. Typically, the person feels uncomfortably hot and sweats excessively.
Compared to heat illnesses like heatstroke, heat intolerance is usually a symptom of endocrine disorders, drugs, or other medical conditions, rather than the result of too much exercise or hot, humid weather.
In patients with multiple sclerosis (MS), heat intolerance may cause a pseudoexacerbation, which is a temporary worsening of MS-related symptoms. A temporary worsening of symptoms can also happen in patients with Postural Orthostatic Tachycardia Syndrome (POTS) and Dysautonomia.
Diagnosis is largely made from the patient history, followed by blood tests and other medical tests to determine the underlying cause. In women, hot flashes must be excluded.
Excess thyroid hormone, which is called thyrotoxicosis, is the most common cause.
Other causes include:
Amphetamines along with other types of stimulant medications, such as appetite suppressants
Anticholinergics and other drugs that can impair sweating
Caffeine, menopause, multiple Sclerosis (MS), fibromyalgia, diabetes, hypothalamic tumors, methadone treatment, dysautonomia,
Postural Orthostatic Tachycardia Syndrome (POTS), Sensory Defensiveness/Sensory Processing Disorder.
Treatment is directed at making the affected person feel more comfortable, and, if possible, resolving the underlying cause of the heat intolerance.
Symptoms can be reduced by staying in a cool environment. Drinking more fluids, especially if the person is sweating excessively, may help.