Heat intolerance is a feeling of being overheated when the temperature around you rises. It can often cause heavy sweating.

Heat intolerance usually comes on slowly and lasts for a long time, but it may also occur quickly and be due to a serious illness.

Sensitivity to heat; Intolerance to heat

Heat intolerance may be caused by different factors:

Some types of medicines may make you less tolerant to heat. Not all medicines will affect everyone the same. If you have questions about any medicines you take, contact your health care provider. The types of medicines that may increase your risk of heat intolerance include:

• Antihistamines
• Amphetamines or other stimulants, including those found in drugs that suppress your appetite
• Antibiotics
• Antidepressants
• Antipsychotic medicines
• Blood pressure medicines
• Cholesterol medicines (statins)
• Decongestants
• Diabetes medicines
• Overactive bladder medicines
• Pain relievers (non-steroidal anti-inflammatories, also called NSAIDs)
• Parkinson disease medicines

Certain health conditions may make you less tolerant to heat. This can be due to the condition itself or any medicine you may take to manage it:

• Cystic fibrosis
• Diabetes
• Cardiovascular disease
• Graves disease
• Mental health conditions
• Multiple sclerosis
• Obesity
• Too much thyroid hormone (thyrotoxicosis)

Other issues and conditions can make you more likely to have heat intolerance. These include:

• Alcohol use
• Bacterial or viral infection
• Having had heat exhaustion or heat stroke before
• Illegal drug use (opioids, cocaine, methamphetamines)
• Lack of physical fitness
• Menopause
• Pregnancy

Age can also be a factor. Young children and older adults are less able to adjust to temperature extremes. Older adults are also more likely to be taking medicine that increases the risk for heat intolerance.

Exposure to extreme heat and sun can cause heat emergencies or illnesses. You can prevent heat illnesses by:

• Drinking plenty of fluids
• Keeping inside room temperatures at a comfortable level
• Limiting how much time you spend outdoors in hot, humid weather

Contact your provider if you have unexplained heat intolerance.

Your provider will take a medical history and perform a physical examination.

Your provider may ask you questions like these:

• When do your symptoms occur?
• Have you had heat intolerance before?
• Is it worse when you exercise?
• Do you have vision changes?
• Are you dizzy or fainting?
• Do you have sweating or flushing?
• Do you have numbness or weakness?
• Is your heart beating fast, or do you have a rapid pulse?
• Are there any medicines or drugs that may be involved?

Tests that may be performed include:

• Blood studies
• Thyroid studies (TSH, T3, free T4)

Hollenberg A, Wiersinga WM. Hyperthyroid disorders. In: Melmed S, Auchus RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 12.

Pearce EN, Hollenberg AN. Thyroid. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 207.

Sawka MN, O'Connor FG. Disorders due to heat and cold. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 95.