Record-setting heat has gripped much of the U.S. West and Southwest in recent weeks, and now the East Coast is baking, too.

Temperatures from Washington, D.C., to Boston are expected to soar into the 90s Wednesday, and possibly for several days straight days after that. Combined with humidity, the air could feel more like 100 or higher in some locales, according to the U.S. National Weather Service.

With these high temperatures come significant health threats, says a physician from the Rowan University School of Osteopathic Medicine, in Stratford, N.J.

Get Breaking News Delivered to Your Inbox

"Any extremes in weather can be inherently dangerous, but the initial heat waves every summer can be particularly perilous to those who are most vulnerable to heat-related illnesses, including children, the elderly and those with chronic medical conditions," Dr. Jennifer Caudle, an assistant professor at Rowan, said in a university news release.

Most people can adjust to swings in temperature within about a week, but some people may need twice as long to adjust, Caudle said.

"When the weather changes quickly, such as with a sudden heat wave, our bodies race to help maintain a normal body temperature by adjusting blood flow and sweating," she said.

"The bodies of infants and the elderly aren't able to make those changes as easily as healthy adults, leaving them at higher risk for serious illness and even death," Caudle explained.

Extreme heat claims an average of 658 lives in the United States each year, according to the U.S. Centers for Disease Control and Prevention. In most cases, these deaths occur in homes without air conditioning.

"Many older individuals have medical conditions or live in situations that make them more likely to succumb to the heat," Caudle said.

Besides their inability to adjust quickly to changing temperatures, older folks are less likely to sense and respond to changes in temperature, she said. They also "can have a diminished thirst reflex that keeps them from drinking adequate amounts of liquid," she added.

Safety and financial concerns might also keep seniors behind closed windows without fans or air conditioners, she pointed out.

Kids suffer from the heat, too, and should never be left alone in a parked car.

So far this year, at least 15 U.S. children left in cars have died from heat-related illnesses, Caudle said. Temperatures inside cars can rise by 20 degrees in just 10 minutes, she noted.

"If you find a child asleep in a parked car, don't assume that child is merely napping," she said. "Lethargy and confusion are signs of heat exhaustion or heat stroke, and are urgent medical conditions." Her advice: Remove the child from the car and call 911 immediately. A high body temperature could lead to permanent brain and organ damage.

If the thermometer climbs in your region, Caudle offers some other safety tips:

Kids should avoid outdoor activities between 10 a.m. and 3 p.m., when the sun is hottest.

Wear and reapply sunscreen frequently.

Make sure children drink plenty of water since they dehydrate more quickly than adults.

Check on older relatives and neighbors twice daily during hot weather.

Make sure older people wear loose, lightweight clothing.

Avoid caffeinated or sugary drinks, which can worsen dehydration.

If seniors prefer to remain indoors but don't have air conditioning, take them somewhere cool such as a mall or library.

Move anyone showing signs of heat-related illness to a cool area, Caudle added. Give them plenty of cool, caffeine-free, nonalcoholic liquid every 10 to 15 minutes.

Warning signs of heat illness include excessive sweating, dizziness, weakness, nausea, red or hot skin, fainting, confusion, and trouble with coordination or balance.

Seek immediate medical help if these symptoms don't improve quickly or get worse. Heat stroke can be fatal if not treated right away, Caudle said.