Heatstroke occurs when the body fails to regulate its own temperature and body temperature continues to rise, often to 105F 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 104F 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 102F 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 a child has stopped breathing, begin rescue breathing.
• Do not give aspirin or acetaminophen to reduce a high body temperature that can occur with heatstroke. These medicines 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 [32fl oz to 64fl oz over 1 to 2 hours] for hydration. Most people with heatstroke have an altered level of consciousness and cannot safely be given fluids to drink. You may have to help. Make sure the person is sitting up enough so that he or she does not choke.