Most people—especially those of us who know how muggy and hot Nebraska summers can be—have suffered from heat exhaustion at least once. It usually hits us after we’ve spent too much time outdoors in the blazing sun and haven’t been drinking enough fluids to keep us properly hydrated.

Heat exhaustion is pretty easy to recognize. Muscles cramp up, fatigue sets in, and sometimes lightheadedness or fainting can occur. But never write off heat exhaustion as “not that big of a deal” because it can be a precursor to a more serious heat injury called heat stroke.

Robert Muelleman, M.D., Chair of Emergency Medicine in the Department of Emergency Medicine at UNMC, explains that heat stroke usually causes alteration or damage to a person’s mental state. “It could be as mild as confusion or as severe as seizures,” he says. “Heat stroke damages a lot of different organs—brain, heart, liver, kidneys. That’s why it can be so deadly.”

Dr. Muelleman categorizes heat stroke into two types: classic heat stroke and exertion heat stroke. “Classic heat stroke is the one you read about during a heat wave in the summer. It typically affects elderly people with chronic medical conditions, like diabetes, hypertension, or emphysema. The issue there isn’t necessarily the daytime highs but rather the nighttime lows. If the temperature doesn’t drop below 80° for 72 hours, that’s when we’ll see classic heat stroke. The body doesn’t have a chance to cool down.”

“Heat stroke damages a lot of different organs—brain, heart, liver, kidneys. That’s why it can be so deadly.” - Robert Muelleman, M.D., UNMC

Exertion heat stroke, however, can happen to anybody, and it doesn’t even have to be that hot outside. It’s more about the heat index, explains Dr. Muelleman. “Heat index takes into account the humidity. If the heat index rises above 105°, then everyone is at risk. If it rises above 115°, then athletic and outdoor events really should be canceled.” With exertion heat stroke, it’s a matter of whether or not your body is unable to dissipate the heat or is generating too much heat.

When the body’s temperature control is overwhelmed, it can’t effectively cool down the body. Sweating is the normal response to overheating, but several factors can inhibit the body’s ability to cool itself—things like high humidity, obesity, fever, mental illness, poor circulation, heart disease, sunburn, and prescription drug or alcohol use.

Healthy children and adults are susceptible to heat stroke exertion in the summer because working in the heat or participating in summer sports can put them at risk. Babies, too—especially those left in cars when it’s hot. “Car temperatures rise so fast,” Dr. Muelleman says. “It’s extremely dangerous to leave a baby in the car during the summer.”

As for the symptoms of heat stroke, the Mayo Clinic recognizes the following:

• High body temperature—usually 104°F (40°C) or higher
• Lack of sweat
• Nausea and vomiting
• Flushed skin
• Rapid breathing
• Racing heart rate
• Headache
• Confusion
• Seizures
• Unconsciousness
• Muscle cramps or weakness

If you suspect someone is suffering from heat stroke, immediately call 911 or transport them to the hospital. Any delay seeking medical help can be fatal. While waiting for aid, move the person to an air-conditioned environment and attempt to cool them down by removing unnecessary clothing, fanning air over them, wetting skin with cool water from a cloth or sponge, or applying ice packs.