2023 had the highest number of heat-related deaths, according to a new study. Here are the heat illness symptoms to watch for.

A new study on heat-related deaths in the U.S. between the years 1999 and 2023 found that last year — the hottest year on record — had the most number of deaths in which heat was cited as an underlying or contributing cause. In 2023, 2,325 heat-related deaths were reported in the U.S., compared to just 311 in 2004. Researchers also found that heat-related deaths have more than doubled since 1999, a trend they say is "likely to continue" as climate change drives temperatures up.

It's easy to forget about the risk of heat exhaustion or sunstroke when you're enjoying a pool party or hanging out at the beach, but these serious conditions can and do happen. Ahead, three emergency room physicians answer questions about how to stay safe when it's scorching out — from being able to identify symptoms to the most effective ways to keep cool.

Why should I care about heat illness now?

Summer is when temperatures are the highest in the U.S. As temperatures soared last year, so did ER visits for heat illness. A study from the Centers for Disease Control and Prevention published in April found that there were nearly 120,000 heat-related emergency room visits in 2023, and 90% of them happened between May and September.The most ER visits happened in Arkansas, Louisiana, New Mexico, Oklahoma and Texas, with males and adults between the ages of 18 and 64 having the highest rates of ER visits for heat illness.

Heat is also the deadliest form of extreme weather, the National Weather Service warns. Hot weather kills 1,220 people annually, according to the CDC. And tolls are rising each year, amid climate change. Last year was the hottest in human history, and a record-breaking 2,303 people died from heat exposure, the Department of Health and Human Services estimates.

"With hotter summer months rapidly approaching, it’s important to plan ahead to protect yourself and others from heat illness," Dr. Marc Taub, an emergency physician and medical director of emergency services at MemorialCare Saddleback Medical Center in Laguna Hills, Calif., tells Yahoo Life. "It’s especially important to take precautions for those who are more vulnerable to the heat, such as children, older adults, pregnant persons, those who work outdoors, people without ready access to cool areas and fluids and people with underlying health conditions."

• Read more: Extreme heat can be dangerous for kids. Here's how to keep them safe in high temperatures.

What exactly is heat illness?

Heat illness (also known as heat-related illness) is an umbrella term used to describe several conditions that can happen to your body when temperatures rise.

Heat illness generally refers to these conditions:

• Heat cramps: These can be the first sign of heat illness, and usually involve painful muscle cramps that can happen in the legs and abdomen, per the National Weather Service (NWS).

• Heat rash: This is skin irritation that can happen when you sweat a lot on hot, humid days, the Centers for Disease Control and Prevention says.

• Heat exhaustion: Heat exhaustion is the body's response to an excessive loss of water and salt that usually happens from sweating a lot, according to the CDC. It can cause heavy sweating, fatigue and dizziness, along with other symptoms.

• Heatstroke: Also known as sunstroke, this is the most serious heat illness, the CDC says. It happens when the body can no longer control its temperature. The sweating mechanism fails, and the body is no longer able to cool down. Body temperature can also get to 106 degrees or higher within 10 to 15 minutes, according to the CDC. Heatstroke can lead to permanent disability or death.

Read more: What does a heat rash look like? How to identify and treat it

What are the symptoms?

Symptoms of heat illness vary depending on the type you experience. Here's a breakdown, according to the CDC:

Heat cramps

• Muscle cramps in the abdomen, arms or legs

• Pain in the abdomen, arms or legs

• Spasms in the abdomen, arms or legs

Heat rash

• Red clusters of pimples or small blisters

• Pimples or blisters that show up on the neck, upper chest, groin, under the breasts and in elbow creases

Heat exhaustion

• Headache

• Nausea

• Dizziness

• Weakness

• Irritability

• Thirst

• Heavy sweating

• Elevated body temperature

• Urinating less than usual

Heatstroke

• Confusion, altered mental status, slurred speech

• Loss of consciousness

• Hot, dry skin or excessive sweating

• Seizures

• Very high body temperature

How dangerous is heat illness?

It depends on the type of heat illness you have. Heat rash and heat cramps are "generally uncomfortable if you are healthy," Dr. Lewis Nelson, chair of emergency medicine at Rutgers New Jersey Medical School, tells Yahoo Life. However, they are not usually serious.

But anyone can experience heat exhaustion and heatstroke — the latter of which is life-threatening, he points out.

"With heatstroke, you can develop organ problems, kidney failure, heart problems and stroke-like symptoms," Dr. Eric Adkins, emergency medicine physician at The Ohio State University Wexner Medical Center, tells Yahoo Life. "You can die from heatstroke."

I am having symptoms. What should I do?

Doctors recommend getting out of the heat ASAP if you don't feel well. "The most important intervention if you feel sick in the heat is to move to a cooler area," Nelson says. "This may be as simple as moving out of the sun or going indoors."

Using a fan can speed up the evaporation of sweat and help you cool down, but Nelson points out that it's "not very efficient" at higher temperatures. In fact, the Environmental Protection Agency recommends that people don't use fans when the heat index temperature, which is a combination of the temperature and humidity, is above 99 degrees Fahrenheit.

"Making sure you are adequately hydrated is critical and replacing the lost sweat with water, plus electrolytes will help avoid a fall in your blood sodium level," Nelson says.

It's also a good idea to take off extra clothes and put on wet towels, if you have them nearby, to help cool you down, Adkins says. Spraying water on your body can also help, according to Taub.

If someone is showing symptoms of heatstroke, call 911 immediately. The NWS also urges getting "immediate medical attention" if heat cramps last for more than an hour, the person vomits or if heat exhaustion symptoms get worse or last for more than an hour.

How can I stay informed about heat risks?

The CDC just launched a Heat & Health Tracker to make it easier to know what's happening with heat in your area. The tracker offers local heat and health information, including rates of emergency room visits for heat illness where you live. The CDC also notes which medications might make you more vulnerable to the effects of heat, and how to store them safely when temperatures rise.

"Keep track of daily weather forecasts and local heat alerts," Taub says. "Good sources of information on current and forecasted weather include local news channels and weather websites." He also suggests checking out Heat.gov for up-to-date information and forecasts.

My car is always sizzling in the summer. How can I keep myself cool?

Car temperatures can skyrocket, and research has found that interior temperatures can hit 116 degrees and seats can get up to 123 degrees.

"Getting into a hot car for a brief period of time is generally safe, but opening the windows or turning on the air conditioning should help moderate the temperature," Nelson says. "The inside of a car, especially in the sun, can reach unsafe temperatures if not cooled, so do not keep children or pets in closed cars, even if out of the sun."

Adkins recommends parking in the shade when you can. A sun shade in your car can help to deflect heat away from the interior as well, Taub says. If your car doesn't have air conditioning and it's extremely hot outside, Adkins suggests taking public transportation if it's available.

What are the most effective ways to stay cool?

If you feel yourself getting hot, there are a few things you can do to cool off in the moment.

Drinking plenty of water is an obvious choice, but Adkins also recommends keeping an eye on the color of your urine. "If it looks more pale yellow, you're hydrated," he says. "If it's dark yellow, orange or brown, that's a primary sign of dehydration."

Using fans, including portable fans, when the heat index is below 99 degrees can be helpful, along with misting yourself with cool water, Nelson says. Putting cool, wet cloths on your wrists, neck and ankles can help keep your temperature down, too, Adkins says.

Is there anything else I can do?

Doctors say there are a few other moves you can make to keep yourself cool on hot days. A big one is avoiding being outside on the hottest times of the day — typically between 10 a.m. and 2 p.m. — if you're able, Adkins says.

Nelson also suggests carrying around a bottle of water with you to make sure you're staying well hydrated. Carrying a portable fan in your bag and using it when you need to cool off can also be helpful, according to Adkins.

If you want to really plan ahead, Adkins recommends planting trees on your property to create shade for the future.

Overall, doctors stress the importance of being aware of the heat in your area and taking steps to keep yourself cool. "Exposure to excess heat can be serious — and it's important to take it seriously," Adkins says.

This article was originally published on May 22, 2024 and has been updated.