Extreme heat

What is it, and who’s most affected by it?

Extreme heat

What is it, and who’s most affected by it?

Extreme heat

Hotter and/or more humid than average for a particular location and time; or above 90 F for at least 2 to 3 days

Heat domes

Hot air trapped over a large area that causes high temperatures and sets the stage for heat waves

Heat waves

Prolonged periods of excessively hot weather, accompanied by high humidity

Extreme heat is becoming more common in the era of climate change, and it affects every bodily system.

“Extreme heat is becoming more common in the era of climate change, and it affects every bodily system,” said David Terca, MD, emergency medicine assistant chief for Kaiser Permanente in Northern California.

“It especially affects children and the elderly, but really everybody’s system and every illness can be affected by extreme heat.”

According to Dr. Terca, extreme heat can make certain health conditions like asthma, COPD (chronic obstructive pulmonary disease), and diabetes worse.

Prevent and recognize heat-related illness


Occurs when you lose more fluids than you’re taking in.

Symptoms: Decreased urination, dry mouth, fatigue, confusion, dizziness, and heart palpitations

Heat cramps

May be an early sign of heat exhaustion or heat stroke.


Symptoms: Muscle pains or spasms, usually in legs and abdomen; often occurs during strenuous activity in extreme heat

Heat exhaustion

Is a mild heat-related illness due to high temperatures and inadequate or unbalanced replacement of fluids.


Symptoms: Cold, pale, and clammy skin; heavy sweating; muscle cramps; loss of consciousness


If you experience signs of heat exhaustion, move to a cooler area, wear lightweight clothing, drink water, and rest.

Heat stroke

Can occur if symptoms of heat exhaustion persist for more than 1 hour, worsen, or include vomiting. It’s a serious heat-related illness that occurs when your body is unable to regulate its own temperature.


Symptoms: Hot, red, dry, or damp skin; a body temperature of 103 F or higher; confusion; loss of consciousness 

Cardiac events

Caused by the interaction between heat and cardiovascular disease contribute to about a quarter of heat-related deaths, according to the Environmental Protection Agency. Cardiac events include heart attacks, heart arrhythmias (irregular heart rhythm), and heart failure.


Symptoms: Watch for symptoms of heat-related illness and heart attack warning signs


If you’re having symptoms or if things don’t feel right, be proactive in seeking medical help immediately.

Are you or a family member at a higher risk?

Protect yourself and your family

Stay hydrated Even if you’re not thirsty, be sure to drink plenty of water. Avoid caffeinated, sugary, or alcoholic beverages, which can cause dehydration.
Stay cool Remain indoors in air-conditioned areas. If your home isn’t air-conditioned, visit public libraries and shopping centers, or your nearest cooling station.
Dress to beat the heat Wear lightweight, loose-fitting clothing and take cool baths or showers to reduce your body temperature.
Limit outdoor activities Avoid going outside between 10 a.m. and 4 p.m., when the sun’s rays are strongest. Complete outdoor activities, including exercise, during the mornings and evenings. If you can’t avoid outdoor activities, wear a wide-brimmed hat, remain in a shady area, and take frequent breaks.

Find resources

Sign up for emergency alerts in your area. State emergency management offices for Kaiser Permanente areas are:

If you’re unable to afford your cooling costs, weatherization expenses, or energy-related home repairs, contact the Low Income Home Energy Assistance Program for help.

Find assistance programs in your area using the Kaiser Permanente Community Support Hub.

The Centers for Disease Control and Prevention’s Heat & Health Tracker provides local information and data.

The American Red Cross has more tips on what you should do before, during, and after extreme heat events.

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