Heatstroke occurs when the body fails to regulate its own temperature and body temperature continues to rise, often to 105 F or higher. Signs of rapidly progressing heatstroke include:

• Unconsciousness for longer than a few seconds.
• Convulsion (seizure).
• Signs of moderate to severe difficulty breathing.
• A rectal temperature over 104 F after exposure to a hot environment.
• Confusion, severe restlessness, or anxiety.
• Fast heart rate.
• Sweating that may be heavy or may have stopped.
• Skin that may be red, hot, and dry, even in the armpits.
• Severe vomiting and diarrhea.

Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or result in serious, long-term complications. After calling 911 or other emergency medical services, follow these first aid steps.

• Move the person into a cool place, out of direct sunlight.
• Remove the person's unnecessary clothing, and place the person on his or her side to expose as much skin surface to the air as possible.
• Cool the person's entire body by sponging or spraying cool-not cold-water, and fan the person to lower the body temperature. Watch for signs of rapidly progressing heatstroke (below).
• Apply ice packs to the groin, neck, and armpits, where large blood vessels lie close to the skin surface. Do not immerse the person in an ice bath.
• Check the person's rectal temperature frequently, and try to reduce it to 102.3 F or lower as soon as possible. The longer the body is at a high temperature, the more serious the illness and the more likely it is that complications will develop. Temperatures taken by mouth or in the ear are not accurate in this emergency situation.
• If breathing stops, start rescue breathing.
• Do not give aspirin or acetaminophen to reduce a high body temperature that can occur with heatstroke. These medications may cause problems because of the body's response to heatstroke.
• If the person is awake and alert enough to swallow, give the person fluids [32 fl oz to 64 fl oz] within the first 2 hours for hydration. However, a person with heatstroke may have an altered mental status and may not be able to safely drink fluids without help.