As the temperatures have plummeted across northern Ontario to well below zero, Sudbury’s health unit is reminding people to cover up any exposed skin if they can.

Health unit spokesperson Allan McDougall said hypothermia and frostbite can happen fast and should be treated properly.

"The worst thing you can do is rub it because if the skin structure if frozen, you can break down the cell structure," he said. "So, ideally, gradually warm it."

McDougall says hypothermia occurs when someone's internal body temperature drops and the body can't warm up on its own. He says someone with hypothermia should be brought inside to warm up and seek medical attention if necessary.

Wind is chilling

With the region passing through an extreme cold snap, those who work with the homeless are keeping a close eye on the most vulnerable.

The city of Sudbury changed the criteria for Extreme Cold Weather alerts this season to take into account the effect of wind chill. Before, 24-hour-a-day warming centre services only kicked in if the temperature dropped below -15C.

Now, an extreme cold weather alert is issued whenever the wind makes it feel like -20C or colder.

The co-ordinator with the Homelessness Network in Sudbury said the change has already resulted in more help for the homeless.

"I counted for November and December. There were actually four days that met the criteria of -20C," Lianne Bergeron said.

The Elgin Street Mission is Sudbury's warming centre.

Staff members keep in close touch with regular users when temperatures are so extreme, said Pastor Rene Soulliere, who runs the mission.

"When somebody doesn't show up here, we want to know where they are," he said.

"There has been times when we've even called the police and asked them if they can track them down. They're regulars and we're not seeing them."

Souliere said between 10 and 20 people are spending their nights at the mission when the temperatures plummet.