This week's heat wave is doing more than just making people uncomfortable. The heat index, or what the air actually feels like when you combine temperature and humidity, is climbing past 105 degrees in some areas.

That number is a critical threshold. Once the heat index crosses 105, the body's natural cooling systems can start to fail.

Normally, your body cools itself by sweating, but when humidity is high enough that sweat can't evaporate efficiently, the body struggles to release heat at all. "Essentially, your body's ability to evaporate the sweat off of you stops working when your body temperature reaches 105 degrees," says Austin Krohn with the Columbia Boone County Public Health and Human Services.

This danger isn't limited to outdoor workers or athletes. Anyone, regardless of age or health, can be affected when the body loses its ability to cool itself down. Young children, older adults, and people with chronic health conditions face an even higher risk.

"This is really where the heat can come down to anyone," Austin says, You could be the healthiest, most in-shape person you've ever been." Warning signs to watch for include heavy sweating that stops, dizziness, nausea, confusion, and a rapid heartbeat.

If sweating stops entirely while someone is still overheated, that's a sign the body may be slipping into heat stroke. "It requires immediate medical attention. You have to dial 911. Hopefully someone's around if you or a loved one is suffering from heat stroke." Austin says.

Don't wait until you feel sick to take the heat seriously. Stay hydrated, take frequent breaks in the shade or air conditioning, and check on neighbors who may not have reliable AC.