Sainte-Justine Hospital has issued a bitter warning about the dangers of frostbite.

The children’s hospital posted photos on Facebook of children with red, swollen, blistered feet – a result of the harsh temperatures.

“Intense cold can quickly cause frostbite. Young children are particularly at risk. Keep them warm and dry,” the post read.

Frostbite occurs in cold temperatures as blood vessels close to the skin constrict to protect the core body temperature.

When your body is exposed to the cold for a long period of time, blood flow to the extremities – in particular hands, feet, nose and ears, can be severely restricted, leading to frostbite. 

Liane Fransblow, trauma coordinator of the Montreal Children's Hospital's injury prevention program, said the hospital has received a "handful" of frostbite cases over the past week. With temperatures forecasted to dip as low as -20 again over the weekend, she offered advice to parents on how to keep their kids safe from the cold. 

"If it's less than -20, -25, don't play outside, stay indoors as much as you can. If you have to go outside to go somewhere, stay bundled up," she said. "For kids, make sure their ears, nose, hands and toes are warm. Neckwarmers, hats, gloves, mittens... Make sure there's no holes in their boots, so snow doesn't go in and make sure none of their clothing is wet."

Fransblow warned that younger children need to be especially closely monitored as they're unable to vocalize their specific discomfort. 

"Some of the older, younger children won't want to tell you, because they don't want to come inside, so you have to be the adult and check for them and make them come inside at regular intervals to warm up," she said. 

People heading outside are warned to wear layers and cover as much as exposed skin as possible to prevent frostbite.

Mild frostbite makes skin appear yellowish or white but is still soft to the touch. Skin might turn red as it warms before returning to normal.

Treat mild frostbite by moving to a warm room, wrapping in blankets and using skin-to-skin contact. Heat can be carefully applied to the frostbitten area, but use caution not to burn the skin.

Thawing frostbitten skin is very painful, explains Environment Canada, adding that the injured skin should be placed in water that is just above body temperature.

Never rub, massage or shake the injured skin – that can cause more damage.

Severe frostbite can cause permanent damage to body tissue. It requires immediate medical attention, according to Environment Canada.

In severe cases, frostbitten skin becomes discoloured and turns black.

Nerve damage may occur and become so severe that feeling is lost in the region. Patients will also develop blisters.

If the skin is broken and becomes infected, gangrene can set in which can result in amputation of the affected areas.