On the first day of summer, the Southwest region of the United States is expected to swelter, with some regions experiencing temperatures over 120°F (49°C). To keep residents safe, officials are warning of the health dangers associated with the extreme heat.

The National Weather Service (NOAA) has issued an “excessive heat warning” for Las Vegas and nearby areas through June 23.

In the Las Vegas Valley, the high temperatures are expected to reach 117°F (47°C), while in Death Valley and the Colorado River Valley the mercury is expected to pass 120°F (49°C).

“A prolonged period of near record-to-record heat will create a dangerous situation in which heat illnesses are likely — especially for the elderly, children, homeless, those unaccustomed to the heat, and those that do not take proper precautions,” NOAA in the warning.

Extreme weather and extreme consequences

Heat waves are especially deadly in the United States where they account for most weather-related deaths, according to the .

“From 1999 through 2009, extreme heat exposure caused or contributed to more than 7,800 deaths in the United States,” the CDC reported.

A single heat wave can result in hundreds or even thousands of deaths. In 1995, a heat wave in Chicago was estimated to have caused at least 650 deaths. And in 2003, a heat wave left 14,800 dead in France, according to the CDC.

In the Southwest, where the heat is so intense that airlines have reportedly , doctors have warned that the extreme temperatures can lead to unexpected injuries like second and third degree burns.

Read More: How to find out if you have summer SAD »

Dr. Kevin Foster, of the Arizona Burn Center, said in a that asphalt, concrete, and playground equipment can cause serious burns.

“Young children are particularly vulnerable,” Foster said. “Not only is their skin more sensitive, but they haven’t learned how to remove themselves from the hot surface or object. Though they might be uncomfortable on the hot surface, they don’t understand why they are hurting or that they need to move.”

Foster warned that even the interior of a car could be dangerous for children to touch when temperatures outside exceed 100°F (38°C).

The Southern Nevada Health District is warning residents to take steps to protect themselves. While under normal conditions the body can cool itself naturally via sweat, the district that “extreme heat causes the evaporation process to slow and the body to work harder to maintain a normal temperature.”

Those most at risk include people over the age 65, and children, whose bodies are not very adept at regulating temperature. Additionally, people who are overweight, on certain medications, and who live in cities where temperatures can be warmer are also at increased risk.

Warning signs of heat exhaustion and heat stroke

The high temperatures can cause a host of injuries from somewhat minor symptoms such as heat cramps and rashes, to more serious conditions like heat exhaustion and heat stroke.

Symptoms of heat exhaustion, which occur when the body loses an excessive amount of water and salt via sweat, include tiredness, muscle cramps, nausea, vomiting, and dizziness.

Read More: Hot weather causes more than sunstroke »

While heat exhaustion and heat stroke are two separate conditions, they are related. Heat exhaustion can be a precursor to heat stroke, which occurs when the body’s temperature quickly rises, and the sweat mechanism designed to cool the body falters.

This condition can result in serious symptoms like a throbbing headache, dizziness, nausea, and a rapid, strong pulse. It can be life-threatening for people who don’t seek treatment quickly.

Should a person appear to have heat stroke, the Southern Nevada Health District advises calling an emergency line, using wet towels and fans to cool the person, and putting them in shade or a cool shower. They do not advise giving fluids.

Read More: Tips for beating the summer heat »

Understanding how to stay safe in a heat wave will increasingly become important, according to the CDC.

“Experts project that as our climate changes, extreme heat events in the United States will become more frequent, longer lasting, and more severe,” CDC officials . “By the end of this century, extremely high temperatures that currently occur once every 20 years could happen as often as every two to four years.”