As extreme heat blankets the country, a visual guide to heat-related illness

Last summer was the hottest in 2,000 years, according to a study published in Nature. We're still a few days from the official start of summer, and the heat is already reaching dangerous levels around the U.S.

This week, residents in parts of the Midwest to the Northeast are expecting temperatures in the mid-90s and triple digits with high humidity. And as temperatures rise in much of the country, so does the risk of heat-related illnesses.

According to the U.S. Department of Health and Human Services, heat-related deaths have been on the rise, from 1,602 in 2021 to 2,302 in 2023.

Here's a look at where the high heat is expected and how to recognize and treat heat-related illnesses.

Temperatures will exceed 90s in most of the East

The National Weather Service warns that dangerous temperatures will reach from St. Louis and Chicago to Pittsburgh, New York City and Boston.

Unable to view our graphics? Click here to see them.

With high temperatures, risk of heat illnesses rises

Excessive heat and humidity make it difficult for your body to regulate its temperature. Understanding the symptoms of extreme heat exposure and managing its effects can be crucial to your health.

Here are some of the signs and symptoms of heat illness, according to the Centers for Disease Control and Prevention.

Heat index chart calculates danger of humidity, heat

The National Weather Service cautions that "extreme heat and humidity will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities."

The graph below illustrates how hot it feels when temperature and humidity are combined.

More:How long does heat exhaustion last? What to know about the heat-related illness.

How to help a victim of heatstroke

According to the CDC, heatstroke can be fatal. The organization's recommendations:

How to help someone with heat exhaustion

Heat exhaustion is considered a less severe condition than heatstroke, according to the CDC. But the agency still suggests some treatments:

Who's at highest risk?

Age, weight, fever, dehydration, heart illness, poor circulation and sunburn all affect a person's capacity to stay cool in hot weather, according to the CDC. Drug and alcohol abuse can have a role as well.

Those at greatest risk of heat illness are people who are:

• Ages 65 and older.
• Ages 2 and younger.
• Suffering from chronic diseases or mental illness.

Young and healthy people can get heat illness if they're active in hot weather, the CDC says.

Tips on keeping cool

• Drink water, more than usual, no matter how active you are. Don't wait until you're thirsty. Make sure your pets have plenty to drink.
• Avoid liquids with large amounts of sugar, alcohol or caffeine. These can increase loss of body fluid.
• Stay in air-conditioned buildings as much as possible.
• Take cool showers or baths.
• Limit outdoor activity, especially in the middle of the day.
• Use drapes or shades on windows to keep out the sun.
• Limit oven and stove use to keep in-home temperatures lower. 
• Wear light-colored, loose-fitting clothing to improve perspiration evaporation.

What else can you do?

• Check on the well-being of friends and neighbors. Do they need help keeping cool?
• Never leave people or pets in a closed car, even with partially open windows. The vehicle interior can rapidly reach dangerous temperatures.
• Seek immediate medical care for those with symptoms of heat illness.

SOURCE Centers for Disease Control and Prevention; Federal Emergency Management Agency; National Oceanic and Atmospheric Administration; Emergency Operations Center, Houston, USA TODAY Network reporting and research