Heat waves are no longer rare events.

Periods of extreme heat now occur more often and last longer, placing serious strain on human health.

1. Dehydration and Fluid Imbalance

One of the earliest and most common effects of heat waves involves excessive fluid loss. High temperatures increase sweating, which removes water and essential salts from the body. When fluid intake does not keep pace with this loss, dehydration develops.

Dehydration reduces endurance, causes fatigue, and limits the body’s ability to regulate temperature. Early signs may include thirst, dry mouth, and reduced energy. Older people face higher risk because the sense of thirst often weakens with age. Drink water regularly throughout the day, even when thirst feels mild. Eating water-rich foods such as fruit can also help maintain balance.

2. Heat Exhaustion and Overheating

Prolonged exposure to high temperatures can overwhelm the body’s cooling system. When internal temperature rises faster than heat can escape, heat exhaustion may occur. This condition often develops during outdoor work, exercise, or poorly ventilated indoor spaces. Symptoms include weakness, dizziness, heavy sweating, and nausea. Without prompt cooling, heat exhaustion may worsen and require medical attention.

Take frequent breaks in shaded or air-conditioned areas. Wear loose, light clothing and avoid intense physical activity during peak afternoon heat.

Dr. Kristie Ebi, a global expert on heat and health, has emphasized the seriousness of extreme heat, stating: “Heat is already the leading cause of weather-related deaths in the United States.” This statement highlights why early recognition and prevention remain critical.

3. Worsening of Ongoing Health Conditions

Heat waves place added strain on people with long-term health conditions. High temperatures increase physical stress, making it harder for the body to maintain stable function. Conditions involving circulation, breathing, or energy balance may worsen during heat exposure.

Follow medical guidance carefully during extreme heat. Keep living spaces cool and monitor changes in energy, alertness, or comfort. Checking indoor temperature becomes especially important during hot nights.

4. Sleep Disruption and Mental Fatigue

Heat waves often interfere with sleep, particularly when nighttime temperatures remain high. Poor sleep reduces the body’s ability to recover and increases irritability and reduced focus during the day. Over several nights, mental fatigue accumulates. Lack of rest also affects judgment and reaction time, raising the risk of accidents. Use fans or cooling systems safely to improve airflow. Lightweight bedding and cool showers before bedtime may support better sleep quality during hot periods.

5. Increased Risk for Outdoor Workers and Athletes

People who work or exercise outdoors face heightened danger during heat waves. Continuous activity increases internal heat production, which combines with environmental heat to raise overall risk. Construction workers, delivery staff, and athletes often experience longer exposure than the general population.

Adjust schedules to cooler morning or evening hours when possible. Employers and coaches should encourage regular rest breaks and access to shade and fluids.

Heat waves pose serious health risks that go far beyond discomfort. Dehydration, overheating, disrupted sleep, and worsening of ongoing conditions all contribute to increased danger during extreme heat. With thoughtful preparation, hydration, cooling strategies, and awareness, many of these risks can be reduced.