What is a Humidex Advisory?
In Canada, the humidex represents the effects that high humidity and high temperatures can have on the body. According to Environment Canada, a Humidex Advisory is issued when temperatures are expected to reach or get higher than 30°C and the humidex values are expected to reach or get higher than 40. The higher the humidex, the harder it is for sweat to evaporate and cool the body. The humidex combines the temperature and humidity into one number to reflect the perceived temperature. Because it takes into account the two most important factors that affect summer comfort, it can be a better measure of how stifling the air feels than either temperature or humidity alone.
Degree of Comfort
20 - 29
| No discomfort|
30 - 39
| Some discomfort |
40 - 45
| Great discomfort; avoid exertion |
46 and over
| Dangerous; high risk of heat stroke|
General recommendations for high humidex ratings:
Humidex of 35 to 39: Certain types of outdoor exercise should be toned down or modified, depending on the age and health of the individual, physical shape, the type of clothes worn, and other weather conditions.
Humidex of 40 and over (extremely high): All unnecessary activity should be limited.
If being outdoors is an absolute necessity, drink plenty of liquids and take frequent rest breaks. In hot, humid conditions, there is a considerable risk of heat stroke and sun stroke.
A heat wave is three or more days of temperatures of at least 32ºC. Unusually hot weather conditions affect the body by pushing it beyond its limits. When temperatures and humidity are high, the body must work extra hard to maintain a normal temperature.
How does heat affect the body?
Generally humans can control their internal temperature in the heat by sweating. However, under conditions of extreme heat and humidity, the body can’t keep up and will suffer from heat stress.
Extreme heat can cause many health problems, including heat cramps, heat exhaustion, heat stroke and more. (If you experience any of these symptoms, seek medical attention immediately.) During a heat wave, everyone is at risk, but some groups are more vulnerable than others. They include:
- young children
- people on dialysis or with chronic diseases (e.g. diabetes, heart disease, respiratory disease)
- people who play sports or exercise outdoors
- people who do strenuous outdoor work for long periods of time
- construction workers (or other outdoor workers)
- people who work in places where heat is emitted through industrial processes (e.g. foundries, bakeries, dry cleaners)
- people taking certain medications (e.g. psychiatric drugs, anti-depressants, some antihistamines, over-the-counter sleep medications)
- the homeless
- pregnant women
- people who are overweight
Heat exhaustion usually occurs after prolonged exposure to heat and/or heavy exercise in the heat resulting in increased loss of body fluids through heavy sweating. The signs of heat exhaustion include:
A person suffering from heat exhaustion needs to be removed from the heat immediately and given water to drink and cool compresses on his or her skin. Fortunately, heat exhaustion is not life threatening, and will resolve with rest, fluids and cooling down.
- clammy, pale skin
- dry mouth
- headache and/or dizziness
Heat stroke is a very dangerous and a potentially life-threatening form of heat stress or injury. The body is so overwhelmed by the heat and humidity that it loses the capacity to sweat. This results in very high body temperature which in severe cases can actually cause brain damage and even lead to death. The signs of heat stroke include:
Heat stroke can occur suddenly and is an emergency requiring immediate medical attention.
- very high body temperature (39ºC/103ºF or higher)
- hot, red and dry skin
- absence of sweating
- deep or shallow breathing
- a weak pulse rate
- confusion or hallucinations
- loss of consciousness
What can you do to prevent heat injury?
- Follow the humidex advisory recommendations.
- Dress young children and babies very lightly, and do not bundle them in blankets or heavy clothing.
- If the weather calls for unusually hot conditions, try and plan your day so you can stay out of the heat.
- Stay cool indoors by taking cool showers or wetting your hands, face and the back of your neck.
- Avoid vigorous exercise in the heat (this includes children as well). If you have a young child or a child with chronic respiratory conditions such as asthma, do not allow them to partake in sporting events or exercise during heat waves especially when there is a heat/humidity advisory in effect.
- Keep your home cool by limiting the use of your oven/stove.
- Turn off unnecessary lights.
- Keep windows slightly open during the day.
- At night, open windows wide to cool the house.
- Never leave children or pets in a parked car.
- Health Canada - Extreme Heat Events
If you have to be outdoors:
- Be aware that children are unable to perspire as much as adults and therefore are more prone to heat stress than adults.
- Limit your activity to morning and evening.
- Give your body's temperature a chance to recover by resting often in the shade.
- Wear a wide-brimmed hat, sunglasses, and light, loose-fitting clothing.
- Drink plenty of water and avoid liquids that contain alcohol, caffeine or large amounts of sugar. It is important to know that children may not feel thirsty but will still need to drink regularly.
- When swimming in a pool or at a beach, be aware that the high humidity and sun rays are still a potential threat. Proper sunscreen protection and frequent rests in the shade are still necessary.
- When in the sun, keep track of how long you or your child has been outside. Learn to recognize the signs of heat exhaustion right away so you or your child can get shelter in order to avoid further heat injury. Also, use common sense and remove yourself or your child from the sun/heat as frequently as you think is necessary. Do not over do it.