High temperatures are not the only concern during a summer heat wave, according to Environment Canada senior climatologist David Phillips, who says humidity plays a major role in how the body handles hot weather.
Phillips said humidity is always present in the atmosphere, but people notice it most when levels rise and create uncomfortable conditions.
He explained that the body cools itself through sweating, but high humidity makes that process less effective because sweat cannot evaporate as easily.
Phillips said heat and humidity can lead to health concerns including fatigue, heat cramps, heat exhaustion and heat stroke, particularly for older adults and infants.
Southern Ontario experienced its first major heat wave of the summer around Canada Day, with humidex values reaching as high as 45 to 48 in some areas.
