(NEW YORK) -- Summer doesn't officially start until Wednesday evening, but in some parts of the country the sweltering summer heat came early as the temperature in Denver and Phoenix eclipsed 100 on Monday. And over the next few days, parts of the East Coast will bake as well.
Thousands of people end up in hospitals because of heat-related illnesses every year and according to the most recent data from the Centers for Disease Control and Prevention, nearly 3,500 people died after exposure to excessive heat between 1999 and 2003.
Despite the dangerously high heat and humidity, medical experts say there are simple but important ways people can stay cool on oppressively hot days and avoid problems like heat exhaustion and heat stroke.
Dr. Jeffrey Rabrich, director of EMS and disaster preparedness at St. Luke's & Roosevelt Hospitals in New York, expects to see quite a number of people come to the emergency room with heat-related symptoms over the next few days as temperatures in New York City climb into the 90s.
"Generally, whenever we have a heat wave or high humidity, we get a lot of patients in with symptoms that include dehydration, lightheadedness and passing out," Rabrich said. "Most people are not too severe and we can treat them by cooling them off and giving them fluids. But every once in a while, we get a couple of cases of heat stroke."
Heat stroke is a life-threatening condition that requires immediate medical attention. Doctors warn it can be caused by being out in high temperatures for too long or by being overly active in very hot weather.
People should monitor themselves and others for the classic signs of heat stroke.
"Watch out for symptoms like fatigue, dizziness, lightheadedness, nausea, or if the skin becomes hot or sweating stops," Rabrich said.
Heat exhaustion is less serious, but if not treated, can progress to heat stroke. According to the American Red Cross, symptoms of heat exhaustion include cool, moist skin, headache, dizziness and nausea.
There are simple steps people can take to avoid experiencing any hot weather symptoms.
"Avoid outdoor activities during the hottest part of the day, typically between 10 a.m. and 4 p.m.," Rabrich said. "People also must stay hydrated by drinking fluids like water or Gatorade."
Avoid alcohol, he advised, since it can act as a diuretic and lead to dehydration.
There is, however, the danger of overhydration -- also known as "water intoxication" -- so Jeffrey Pellegrino, who serves on the National Scientific Advisory Council for the American Red Cross, advised drinking around half a cup of water every 20 minutes or so if out in the heat.
Proper wardrobe choices will also help keep cool -- wear loose-fitting clothing and a hat if out in the sun.
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