According the U.S. Department of Health and Human Services, symptoms of heat stress can include heavy sweating, weakness, clammy skin, fast pulse, and nausea or vomiting.
Early indications of heat stress can include muscle cramps, heat rash, fainting spells and a pulse rate greater than 100 beats-per-minute.
Those suffering from heat stress should lie down in a cool place, with wet cloths applied to the head, neck, armpits and upper legs near the groin area.
People need to be mindful of the most severe heat-related illness, heat stroke, which includes a body temperature over 103°F.
Experts say children and the elderly are especially vulnerable during periods of high temperatures.
HHS said to prevent heat-related illnesses, spend time in locations with air-conditioning if possible, drink plenty of fluids, wear lightweight clothing and limit outdoor activity to morning and evening hours.
For more information, visit the HHS public health emergency preparedness website at http://emergency.cdc.gov/disasters/extremeheat/