With humidex values approaching 40 degrees Celsius in southern Manitoba, a local doctor is urging everyone to stay cool and stay hydrated.

Environment Canada has issued a heat warning. Dr. Denis Fortier says on days like today, our body will have more difficulty in maintaining its normal temperature of 37 degrees Celsius. Dr. Fortier says the systems within our body work well at 37 degrees. But when temperatures become extremely cold or extremely hot, our body struggles and we need to make sure we're not putting ourselves in a situation where it can no longer maintain that normal temperature.

"So in other words, 37 degree humidex levels, that means that we probably want to be staying indoors, keeping cool in various ways," suggests Dr. Fortier.

He notes it is important to keep our water levels up because of the tremendous amount of fluids we are losing through perspiration. For those who work outdoors, he suggests packing extra water, and maybe even including some electrolyte drinks. And those who prefer to exercise outside, Dr. Fortier says you should limit yourself to the very early mornings or late at night when temperatures are not so high.

According to Dr. Fortier, those most at risk on days like today are the very young and the very old. He notes the middle aged should be healthy enough, unless if they have other illnesses, to manage this thermal regulation within the body. But older people often have more difficulty because of illness or medications which makes it tougher to maintain.

Dr. Fortier says early warning signs that someone is over-heating include sweating profusely and becoming very thirsty.

"Those are the early indications that they're pretty hot and you should take that as an indication to find some shelter, some shaded spots or put them inside where there's some air conditioning," suggests Dr. Fortier. "Sometimes if you miss those early symptoms you will find that people tend to be a little bit more tired, sleepy, groggy, and again those are symptoms of the heat that is getting to these people."

And while excessive sweating can be a negative sign, so too can not sweating enough. Dr. Fortier says if your body reaches a point where it stops sweating, it means it is starting to shut down. This can lead to further heating and if you were to take your body's temperature, it would appear you have a fever. Dr. Fortier says that's because your auto thermal regulation is starting to fail.

"And if they do continue to have high temperatures, that can do significant damage to various organs in the body, whether it be your kidneys, or your heart or your brain," he says. "So those are getting into serious conditions."

Dr. Fortier says on days like this, Emergency Rooms in the region are likely to see additional cases of heat related symptoms.