Heat intolerance

Heat intolerance means that warmth affects you more than expected. You may feel too hot in temperatures that other people find comfortable, or you may become unwell after only mild heat or activity.

It is a symptom, not a disease. Possible causes range from hot or humid weather to hormonal changes, medication effects, or an overactive thyroid. Some people sweat heavily. Others do not sweat enough to cool themselves.

Heat intolerance is different from heat exhaustion or heat stroke. Those are heat-related illnesses that develop when the body cannot control its temperature. Heat stroke is an emergency.

You may notice:

• Uncomfortable warmth or flushing
• Heavy sweating, or unusually little sweating
• Tiredness, weakness, or reduced exercise tolerance
• Headache, thirst, nausea, or light-headedness
• A fast or pounding heartbeat
• Irritability or difficulty concentrating in warm places

Symptoms may appear outdoors, in a warm room, during exercise, or after a hot shower. Humidity can make them worse because sweat does not evaporate as easily.

Brief waves of warmth with sweating and facial flushing may be hot flashes. These are common during perimenopause and menopause, but similar sensations can have other causes.

Common explanations include hot or humid conditions, strenuous activity, dehydration, and wearing heavy or non-breathable clothing. A recent illness can also make heat harder to tolerate while you recover.

Hormonal changes during perimenopause or menopause can cause hot flashes, night sweats, and greater sensitivity to heat.

Medicines can affect sweating, fluid balance, alertness, or the body's ability to control temperature. Examples include some antidepressants like sertraline or fluoxetine, antihistamines like cetirizine or loratadine, bladder medicines, stimulants, antipsychotics, and water tablets like furosemide or hydrochlorothiazide called diuretics. Alcohol and some recreational drugs can also increase risk. Do not stop a prescribed medicine without speaking with the prescriber.

Less common causes include:

• Hyperthyroidism: an overactive thyroid, often with sweating, tremor, weight loss, anxiety, or a fast heartbeat
• Reduced sweating: sometimes caused by skin damage, nerve problems, or certain medicines
• Autonomic nerve disorders: conditions affecting automatic functions such as sweating, heart rate, and blood pressure
• Long-term health conditions: including some heart, lung, or neurological conditions that make cooling or physical activity harder

Heat intolerance can become urgent when it progresses to heat exhaustion or heat stroke. This is more likely during prolonged heat, heavy activity, dehydration, or when sweating is impaired.

Arrange a routine appointment if heat intolerance is new, keeps returning, is getting worse, or interferes with sleep, work, exercise, or daily activities. Also make an appointment if it comes with unexplained weight loss, persistent tremor, frequent palpitations, major changes in sweating, or new menstrual changes.

Seek same-day medical advice if you develop dizziness, headache, nausea, marked weakness, or cramps that do not improve after about 30 minutes in a cool place with rest and fluids. Repeated vomiting or a new inability to sweat while overheating also needs prompt assessment.

Call emergency services if heat exposure is followed by:

• Confusion, unusual behaviour, or trouble speaking
• Fainting, collapse, or a seizure
• Loss of consciousness
• Very hot skin with severe illness
• Chest pain or serious difficulty breathing

These can be signs of heat stroke or another emergency. While waiting for help, move to a cooler place, remove excess clothing, and cool the skin with water, cool cloths, or fans. Do not give drinks to someone who is confused or unconscious.

A clinician will ask when the symptom began, what temperatures or activities trigger it, and whether you sweat more or less than usual. They may ask about hot flashes, menstrual changes, recent illness, weight change, thirst, palpitations, tremor, and exercise tolerance.

Bring a list of medicines, supplements, and recreational substances. Include products taken only occasionally, such as allergy or cold medicines.

An examination may include your temperature, pulse, blood pressure, hydration, skin, and thyroid gland. Testing is guided by your other symptoms. For example, blood tests may be used to check thyroid function, blood sugar, blood cell levels, or salts in the blood. Not everyone needs tests.

Treatment depends on the cause. A medicine may need review, but it should not be changed or stopped without professional advice. Thyroid disease, menopause symptoms, dehydration, and reduced sweating each require different approaches.

To reduce symptoms and prevent overheating:

• Choose cool or air-conditioned spaces during the hottest hours
• Wear loose, lightweight, breathable clothing
• Drink regularly during heat or activity
• Increase activity gradually and take cooling breaks
• Use fans, cool showers, damp cloths, or cold packs wrapped in fabric
• Avoid heavy exercise, alcohol, and large hot meals during extreme heat

If you have heart or kidney disease, or have been told to limit fluids, follow your existing fluid plan and ask for individual advice.

Keep track of triggers, sweating changes, associated symptoms, and medicines taken near the time. This record can help identify patterns.

Heat intolerance caused by temporary heat exposure or mild dehydration often improves after cooling, rest, and fluids. Symptoms related to menopause may come and go over months or years.

When an underlying condition or medicine contributes, improvement depends on addressing that factor. People who sweat very little may need ongoing heat-avoidance planning, especially during exercise or hot weather.

Is heat intolerance the same as excessive sweating?

No. You can feel heat-intolerant while sweating heavily, normally, or very little. Sweating is one way the body releases heat, but it is not the only part of temperature control.

Can anxiety make me feel overheated?

Anxiety can cause flushing, sweating, and a faster heartbeat. However, new or persistent heat intolerance should not automatically be attributed to anxiety, especially if you have other physical changes.

Could my medicine be responsible?

Possibly. Several prescription and non-prescription medicines affect sweating, hydration, or temperature control. Ask a pharmacist or prescriber to review your medicines rather than stopping them yourself.

Should I check my temperature?

Checking it can be useful if you feel acutely unwell, but a normal reading does not explain ongoing heat intolerance. Confusion, collapse, or severe illness after heat exposure requires emergency help regardless of a home reading.