Alabama is among 18 states currently under a heat advisory from the National Weather Service.

Heat index highs are expected to soar this week into the triple digits due to a heat dome stretching across the central U.S.

And in order to stay safe in these 18 states, people are urged to limit outdoor activities, stay hydrated, avoid alcohol, and wear light clothing.

“A heat dome will bring near record breaking hot conditions across the South-Central U.S. this week, with cities like Wichita Falls, Dallas, and Kansas City expected to hit 100 °F for the first time this season,” AccuWeather meteorologist Kai Kerkow recently told Newsweek.

“Nighttime temperatures will remain in the mid-70s to low-80s, offering little relief. The heat dome temporarily spreads east later this week.”

According to the Weather Channel, a heat dome occurs when descending air compresses and warms as it drops closer to the surface.

This sinking, warm air causes days-long heat waves and also dries out the ground and the air above it.

Thunderstorms have a tough time sprouting due to the suppressive motion of the air, so drought can begin or worsen under ridges of high pressure that last for longer than a week, the Weather Channel adds.

The air directly under such a system can become still with little to no wind.

This poses health risks to anyone without access to effective cooling or proper hydration.

Heat is the No. 1 weather killer in the U.S., with hundreds of fatalities each year, according to the NWS.

Many of these fatalities occur under heat domes.

Extreme heat can trigger heat-related illnesses, particularly among seniors, young children, and people with chronic health conditions, according to the Centers for Disease Control and Prevention.

Symptoms can range from intense sweating and muscle cramps to dizziness and nausea.

Increasing temperatures can also intensify ground-level ozone pollution, creating further health concerns.

The Alabama Department of Public Health has identified the most common heat-related illnesses as heat cramps, heat exhaustion, and heat stroke.

Heat cramps involve muscle pain or spasms, usually in the abdomen, arms, or legs, and are often paired with heavy sweating.

Heat exhaustion can cause heavy sweating, pale or clammy skin, tiredness, muscle cramps, dizziness, headaches, nausea, vomiting, and fainting. If left untreated, heat exhaustion can become heat stroke, the most dangerous form of heat illness.

Heat stroke, sometimes called sun stroke, is a life-threatening emergency. This can happen when the body’s temperature rises to 106°F or higher in as little as 10 to 15 minutes.

Warning signs include extremely high body temperature, red or hot skin (which may be dry or moist), a strong and rapid pulse, throbbing headache, dizziness, nausea, dehydration, confusion, and even unconsciousness.

Without immediate treatment, heat stroke can cause serious long-term health problems or be fatal. Medical help should be called right away if heat stroke is suspected, according to the ADPH.

To stay safe, officials have urged everyone to:

• Drink plenty of fluids—avoid alcohol and drinks with caffeine.
• Stay inside air-conditioned rooms whenever possible.
• Seek shade or shelter from the sun outdoors.
• Wear a wide-brimmed hat and light-colored, loose-fitting clothes.
• Use sunscreen with at least SPF 15.
• Take cool showers or baths on hot days.
• Reduce or avoid strenuous activity during the hottest hours.
• Never leave people or pets in parked vehicles, even for a short time.