Heat Exhaustion

Heat exhaustion is an illness caused by heat exposure and loss of fluid and salts through sweating.

It often develops during work, exercise, travel, or time outdoors when heat and humidity make cooling difficult. It needs prompt action because ongoing heat exposure can lead to more serious heat illness.

Excessive sweating, thirst, dizziness, headache and nausea are common presentations of heat exhaustion. Some people notice weakness, muscle cramps, a fast heartbeat, or dark urine. Symptoms may start gradually and become more intense if the person remains in the heat.

Confusion, collapse, seizures, or very hot skin are emergency signs that need urgent medical help, as they may indicate heat stroke.

The body normally loses heat through sweating and increased blood flow to the skin. Heavy clothing, limited airflow, high humidity, exertion and not replacing fluid can overwhelm these cooling responses. Alcohol and some medicines can also affect hydration or heat regulation.

Move to a cool, shaded or air-conditioned place, stop activity, loosen excess clothing and cool the skin with air, damp cloths or a cool shower. If the person is awake and can swallow, offer frequent small drinks. Stay with them and observe for worsening symptoms.

Young children, older adults, pregnant people, people with chronic health conditions, and people taking medicines that affect fluid balance may be less able to adapt to heat. People newly exposed to hot conditions also need time to adjust their activity and hydration routine.

A clinician considers the heat exposure, activity, symptoms, temperature and physical examination. They may check hydration, blood pressure, pulse, mental state and blood tests when symptoms are significant or do not improve. The assessment also rules out other causes of dizziness, nausea or collapse.

Cooling and oral rehydration are often used when a person can drink safely and symptoms are improving. Medical teams may provide IV fluid therapy when oral fluids are unsuitable or closer monitoring is needed. Return to heat or strenuous activity only after recovery and advice from a clinician where appropriate.

Rest in a cool environment and rebuild fluids and food intake as tolerated. Review what led to the episode, including timing of outdoor tasks, clothing, breaks and access to water. A previous episode is useful information to share before strenuous work in the heat.

Continued overheating and dehydration can progress to heat stroke, which is an emergency. Do not leave an unwell person alone in a hot place or assume that sweating means they are safe. Worsening alertness is a particularly urgent warning sign.

Plan demanding activity for cooler periods, take regular cooling breaks, wear light breathable clothing and bring adequate drinks. Increase activity gradually when you are not accustomed to the heat. Check on relatives, neighbours or colleagues who may have limited access to cooling.

Urgent care is appropriate when symptoms do not improve quickly with cooling and drinking, or when the person cannot keep fluids down. Primary care can help review recurrent heat symptoms, medicines and conditions that may affect heat tolerance.