Heat dome. Fahren-hell. Urban Meltdown '11. Whatever you call this heat wave, it's annoying. But if you're a small child, the extreme heat can also be dangerous, doctors say .

Children's bodies handle heat differently from adults, notes Dr. Brian Timmons, a professor at the Department of Pediatrics at McMaster University in Hamilton, Ont.

"The heat can be much more dangerous for kids than for adults. That's because their bodies use different strategies for keeping cool," Timmons told CTV's Canada AM Thursday, "and when it's very hot like this and very humid, those strategies work against them, rather than for them."

The main difference between children and adults is that kids sweat less than adults, Timmons explained. They do still sweat, but their bodies rely less on using water evaporation from the skin than adults do.

"So they have to get by on just letting heat leave their bodies naturally. And they can do that because they have more skin relative to their body mass than adults," Timmons explained.

The problem is that on days when the air temperature is higher than normal body temperature – about 37 Celsius – the body has trouble using convection to transfer heat from the skin into the air, especially when there's plenty of humidity in the air too.

That's when heat-related illnesses can crop up. Instead of losing heat, a child's body can actually start absorbing heat. That can lead to a number of illnesses, including heat exhaustion, heat cramps, heat rash and the worst of them all, heat stroke.

Heat exhaustion refers to the common symptoms that often come on as we begin to overheat:

  • fatigue
  • heavy sweating
  • increased thirst
  • lightheadedness or dizziness

Timmons says kids might also complain of headaches, be irritable and might start acting "unlike their normal selves." If heat exhaustion is not relieved by getting out of the heat, it can lead to the much more dangerous heat stroke.

Some kids develop a rash in the heat. Heat rashes are a sign of skin irritation caused by excessive sweating. It can occur at any age but is more common in young children. A heat rash looks like a red cluster of pimples or small blisters. It is more likely to occur on the neck and upper chest, in the groin, and in elbow and knee creases.

The best treatment for heat rash is to provide a cooler, less humid environment and dry off the skin.

Kids are also susceptible to heat cramps. Heat cramps are muscle pains or spasms that occur in the abdomen, arms, or legs caused by heavy sweating and dehydration. The sweating depletes the body of salt and moisture and the low salt level in the muscles cause painful cramps.

Most heat cramps aren't serious, but those with heart problems should seek medical attention. If a child develops heat cramps:

  • Have them stop all activity and sit quietly in a cool place
  • Have them drink clear juice or a sports beverage
  • Do not allow them to return to any activity for a few hours after the cramps subside. Further exertion may lead to heat exhaustion.
  • If the heat cramps do not subside in one hour, seek medical attention

In kids -- and adults too – heat exhaustion can usually be relieved by getting out of the heat, cooling down, and drinking lots of fluids. But if not relieved, the condition can worsen quickly into heat stroke.

"We know that in kids, with a certain level of dehydration, they'll heat up faster. So it's more important to monitor for those signs in kids than for adults," says Timmons.

Heat stroke is a true medical emergency. During heat stroke, a child's body temperature will rise above 40-41 Celsius. They will stop sweating and lose the ability to thermoregulate. Other symptoms of heat stroke include:

  • a throbbing headache
  • dizziness
  • confusion
  • nausea
  • hot, dry skin

The longer that a child's body temperature is above 40°C, the greater the likelihood that he/she will suffer permanent effects, or death. That's why it's important to dial 911 immediately. While waiting for the ambulance:

  • get the child out of the sun
  • undress them as much as possible.
  • try to immerse the child in cool water or spray them down
  • give them cool water to drink if they are coherent
  • if they are losing consciousness, do not give them water since it may cause them to vomit.

Timmons says the most important tip for keeping kids safe during heat waves is to keep them hydrated as best they can.

"That means having a good breakfast with lots of fluids. Give them something to drink when they leave the house," he advises.

Even if you try to keep fruit juices to a minimum, adding juice to water for flavour will ensure that children will drink if, he says.

"Water is very good, but if you want to turn on thirst, things like sports drinks and things with sodium in the drink can turn on thirst," he says.