What are the symptoms of heat stroke?

Spending too much time in hot weather can make you sick. Most heat-related illnesses happen after being out in the hot weather too long. The body cools itself by sweating, but in hot and humid conditions, your temperature may rise faster than your body can cool down. This can lead to heat stroke, the most serious heat-related illness. You can stay safe by learning the signs of heat stroke, what to do if you or others develop symptoms, and how to prevent heat-related illnesses.

Heat stroke is a condition caused by the body overheating, and it can happen if your body temperature rises to 104° F (40° C) or higher. Heat stroke can cause death or permanent disability if emergency treatment is not provided.

According to the Centers for Disease Control and Prevention (CDC), if you have any of these symptoms of heat stroke, it may be a life-threatening emergency:

• An extremely high body temperature (above 103°F)
• Red, hot and dry skin with no sweating
• Rapid, strong pulse
• Throbbing headache
• Dizziness
• Nausea
• Confusion
• Unconsciousness

If you see someone with signs of heat stroke, have someone else call for medical assistance right away while you begin cooling the person. To cool someone with heat-related illness warning signs, take the following actions:

• Get the person out of the heat and to a shady or air-conditioned area.
• Quickly cool the person by immersing them in or spraying them with cool water, placing them in a cool shower, or applying a sponge or damp sheets to them. Fanning them vigorously can also help.
• Do not give the person alcohol, as it can affect body temperature regulation. 

Heat exhaustion is a milder form of heat-related illness. If heat exhaustion is untreated, it may progress to heat stroke. Heat exhaustion can develop after several days of exposure to high temperatures and inadequate intake of fluids. It is important to recognize its symptoms and how to prevent it.

According to the CDC, the warning signs of heat exhaustion include the following:

• Heavy sweating
• Paleness
• Muscle cramps
• Tiredness
• Weakness
• Dizziness
• Headache
• Nausea or vomiting
• Fainting

The CDC recommends that you get medical attention if symptoms worsen or last longer than one hour.

Those most vulnerable to heat stroke and heat exhaustion include:

• Adults 65 years and older
• Infants and children 4 years and younger
• People with chronic medical conditions, such as heart disease and high blood pressure
• People who are overweight
• Those who work or exercise outdoors

Some medications increase the risk of heat stroke and heat exhaustion because they can prevent sweating, reduce blood flow to the skin or affect fluid balance in the body.

The risk for heat-related illness may increase among people using the following medications:

• Certain medications for mental illnesses
• Medications that regulate blood pressure
• Diuretic medications
• Over-the-counter decongestants

Discuss your medications and the risk of heat-related illnesses with your pharmacist. Pharmacists are experts in drug information and can help identify and potentially prevent side effects.

These tips can also help prevent heat exhaustion:

• Keep cool. Air conditioning is the best way to protect against heat stroke. Stay in the shade, especially midday when the sun is the strongest. Fans can also help the body cool down more quickly and effectively.
• Stay hydrated. Drink cool, nonalcoholic beverages and increase your fluid intake in hot weather, regardless of your activity level. Do not wait until you're thirsty to start drinking. If you're on fluid restriction, you should check with your healthcare provider about how much fluid to consume.
• Think safety. Never leave infants, children or pets in parked cars. Know the symptoms of heat stroke and heat exhaustion.
• Be cautious when exercising or playing sports. During heavy exercise in a hot environment, drink enough nonalcoholic, cool fluids each hour so that you maintain your normal urine output and color.
• Wear appropriate clothing. Choose clothing that is made of thinner, lighter materials to help the body stay cool.
• Use sunscreen. Sunburn also causes you to lose fluids and affects your body's ability to cool itself. Generously apply sunscreen to exposed skin at least 15 minutes before going outside and reapply according to the instructions on the package.

Clinically reviewed and updated September 2022.