For heat exhaustion: “Very thirsty, weak, tired, with a lot of sweating." “Sometimes a headache, nausea and vomiting. Heat exhaustion comes first. That leads to heatstroke if not treated properly.”
For dehydration: “Lips and tongue get very dry,” Varma said. “You’re feeling weak and tired. Maybe muscle cramps, and your skin may be paler. Those are the early signs of dehydration.”

Water is the undisputed champ when it comes to fighting heat-related maladies.
“You should be drinking seven or eight glasses of water on a regular basis,” Dr Varma says . “If you’re active, you might double that.”
Gatorade and other electrolyte supplements are OK, Varma says, “as long as you watch the sugar content.”
What to avoid?
“Avoid caffeinated drinks and alcoholic drinks, even if they’re diluted with water,” he said. “Fruit juices, especially for kids, can have a very high sugar content and that doesn’t help.”
Parents should be vigilant about keeping their children hydrated; it’s not something that tends to be high on kids’ priority list when they are outside playing.
For folks of all ages, attire also matters.
“Wear hats; that’s very important,” Varma says. “Wear loose, cotton clothing — lighter colors, because darker colors attract heat.”
Of course there is a common-sense component to this, too. Try to stay in the shade. Take frequent breaks in any prolonged activities. Never leave kids or pets in cars, even for just a couple of minutes.
If signs of heat exhaustion or dehydration begin to appear, move to a cooler environment and drink cool water. Those simple steps help avert the worst-case scenario — heatstroke.