When the heat is as high as it is in many parts of Canada right now, it can be hard to stay cool. High humidity means that sweat on our skin does not evaporate, impeding our bodies’ ability to cool down.

High temperatures can lead to several heat-related illness, some more severe than others. Here’s a look at what to watch for and when it’s time to seek emergency assistance.

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Heat rash

Heat rashes are a common skin irritation caused by excessive sweating. They can occur at any age but is most common in young children.

During hot, humid weather, the skin’s sweat glands can become blocked, trapping perspiration under the skin, leading to swelling and redness that looks like a red cluster of pimples or small blisters. It is most likely to occur on the neck and upper chest, and anywhere where sweat can accumulate such as the groin, under the breasts, and in elbow creases.

What to do: The best treatment is to move to a cooler or less humid environment and to try to keep any affected areas dry.

Watch for other symptoms of heat illness as rashes can be also be a sign of heat stroke.

The rash should clear up on its own, but see a doctor if it doesn’t get better within a few days.

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Dehydration

Intense heat and heavy sweating can easily lead to dehydration. The early signs include fatigue, feeling overheated, dark urine, dry lips, and of course, thirst.

Many will also experience dizziness or light-headedness as dehydration causes a drop in blood volume and thus a drop in blood pressure, leading to the light-headed feel. A high heart rate also can indicate a lower blood volume and thus dehydration.

What to do: The treatment for dehydration is to drink more fluids, but the best way to prevent it is to drink water throughout the day, even if you don’t feel thirsty.

During hot days, drink more water than usual, and avoid alcohol, since it will cause further dehydration.

If you are exercising in the heat, consider drinking a sports drink to replace lost salt. If you take diuretics, or water pills, consult with a doctor on how much water to drink.

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Heat exhaustion

Heat exhaustion is a heat-related illness that can develop after several hours or days of exposure to high temperatures. If left untreated, it may progress to heat stroke.

Typical symptoms include rapid heart rate, profuse sweating, red and warm skin, nausea, dizziness. Other symptoms include swelling, rashes, nausea, and vomiting. Some can develop cramps in the abdominal muscles, arms, or legs, because heavy sweating will deplete the body’s salt levels, which causes muscles to cramp.

What to do: Anyone with the signs of heat exhaustion should be moved to a cool building or into the shade and given water and told to rest. Try to cool the skin with water spray or a wet towel and then fan the skin if possible.

Taking a cool shower or bath can help for a while, but the better option is to move to somewhere air-conditioned. Exposure to air conditioning, even if only for a few hours a day, will reduce the risk for heat-related illness.

Get immediate medical help if the symptoms don’t improve within an hour of cooling, or if vomiting or other signs of heat stroke develop.

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Heat stroke

The most serious heat illness is heat stroke, which is a medical emergency that can lead to brain swelling, heart problems, kidney damage, or death.

It can come on quickly during overexertion on hot days, or develop slowly, after heat exhaustion. Heat stroke shares many of the signs of heat exhaustion but also includes more dangerous symptoms such as fainting, vomiting, confusion, staggering, or delirium. Someone with heat stroke might sweat profusely or develop dry, flushed skin with no sweating at all.

What to do: If any of these symptoms develop, call 911 or seek emergency assistance.

Try to cool the person down while waiting for help by applying cool water and fanning their skin. If available, apply ice or cold packs under the armpits or around the neck.

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Who’s most at risk

Anyone can develop a heat-related illness but some are at higher risk.

Seniors do not handle heat as well because they often don’t sweat as much as younger adults. They might also have chronic medical conditions that affect their circulation, or are taking medications that affect their ability to control temperature.

Children are at greater risk of heat illness because their thermoregulation isn’t as well developed, they sweat less, and they have a higher surface area-to-weight ratio, which means they absorb more heat.

Women who are pregnant are also at greater risk of heat exhaustion or heat stroke, because their bodies must work harder to cool down both them and their unborn baby.

People with heart disease, diabetes, obesity or other chronic illnesses can also succumb to heat-related illnesses because of poor circulation or because their medications can affect their ability to handle heat.

Sources: The U.S. Centers for Disease Control, Healthy Canadians