Many people feel uncomfortable at either end of the temperature range. In most cases, this is due to a normal variation in comfort levels at various temperatures and is no cause for concern. An extreme intolerance to heat or cold, however, may signal the presence of a condition that deserves medical attention.

Heat Intolerance. People commonly complain about the heat, but someone with heat intolerance finds it almost impossible to stay comfortable when the temperature rises. Heat intolerance occurs when the body’s mechanisms for reducing heat—sweating and increasing blood flow to the skin—are impaired. Some of the potential causes for heat intolerance are:

• Medication side effect: Blood pressure medications, decongestants, and allergy medications are some of the most common drugs with the side effect of heat intolerance. A class of high blood pressure drugs known as beta blockers decrease blood flow to the skin, preventing heat from escaping from the body. Antihistamines, such as loratadine (Claritin) can lead to heat intolerance by inhibiting sweating. Decongestants, such as Sudafed, and stimulants used to treat Attention-Deficit Hyperactivity Disorder (ADHD) can cause heat intolerance because they increase muscle movement which raises body temperature.
• Caffeine consumption: Caffeine, found in coffee, tea, and colas is a stimulant that can increase body metabolism which in turn causes a rise in body temperature.
• Excessive thyroid hormone production: Hyperthyroidism is caused by overactivity of the thyroid gland with the production of too much of the hormone thyroxin. This causes the body’s metabolism to increase along with rising body temperature.
• Menopause: Hot flashes are sudden sensations of heat, most intense over the face, neck and chest, caused by a transient dilation of the blood vessels of the skin. Hot flashes are thought to occur in association with a reduction in estrogen that occurs around the time of menopause which upsets the body’s thermostat that is located in the hypothalamus of the brain.

In most cases, addressing the underlying cause for heat intolerance will alleviate the problem. Changing medications to one less likely to cause heat intolerance or reducing caffeine consumption will help restore heat dissipating mechanisms. Hyperthyroidism can be addressed by treatment with radioactive iodine to destroy a portion of the thyroid gland, medications to reduce thyroxin production, or surgery. In the case of menopause, estrogen replacement therapy or waiting until estrogen levels have stabilized helps with heat intolerance symptoms.

Cold intolerance: People with cold intolerance commonly complain of being cold when everyone else is comfortable. It can be defined as an abnormal sensitivity to a cold environment or cold temperatures. In many cases, cold intolerance is simply due to being thin and having little fat to insulate the body. In other instances, cold intolerance can be a sign of a metabolic problem or chronic illness. Some of the most common causes for cold intolerance are:

• Hypothyroidism: The opposite of hyperthyroidism described in the previous section, someone with hypothyroidism does not produce enough thyroid hormone to maintain a normal metabolism level. A lowered metabolism results in less heat production by the body.
•  Disease affecting the hypothalamus: The hypothalamus is a portion of the brain which, among other functions, maintains body temperature. It can be seen as a type of thermostat for the human body. A number of conditions, including malnutrition, anorexia, head injury, and brain tumors can alter normal hypothalamic function, leading to cold intolerance.
• Anemia: A reduction in the normal amount of blood cells, such as can occur with iron deficiency, can lead to cold intolerance. In addition to making someone intolerant of the cold, people with anemia may also complain of having low energy, dizziness, a pounding heart during exertion, and pale skin.
• Chronic severe illness: Addison’s disease, also known as adrenal insufficiency, results from damage to the adrenal glands with lowered production of the adrenal hormones—cortisol and aldosterone. In addition to cold intolerance, features of Addison’s disease include low blood pressure, fatigue, weight loss, and pigmentation of the skin in certain areas of the body. Cold intolerance can also be a symptom with certain types of cancer.

Other illnesses that have been linked to cold intolerance include fibromyalgia, depression, and sleep deprivation. Since cold intolerance is not a disease but a symptom of an underlying medical condition, treatment hinges on managing that condition. In the case of an anemia cause by insufficient iron consumption, taking supplemental iron will restore blood production with improvement of cold intolerance. Hypothyroidism is usually treated with life-long administration of thyroid hormone replacements. By taking hormone replacements, most people with Addison’s disease are able to lead normal lives.

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