With a cold weather alert expected to last through Thursday for London and Middlesex, medical officials want to remind people about how to avoid serious and potentially life-threatening effects.

"With the present conditions we have today, around -30 to -40 with the windchill and -20 temperatures it may take anywhere from 2 to 5 minutes," says Iqbal Kalsi, Environmental Health Manager with the Middlesex-London Health Unit (MLHU).

At -15 C the MLHU issues a cold weather alert and residents should be on alert for signs of hypothermia.

"When you've been exposed for a prolonged period of time, your internal body temperature goes down below your normal core temperature," says Kalsi.

Symptoms of hypothermia include pale skin, lethargy, confusion, hallucinations.

The effects can be very serious.

"A person could go into a coma and that could cause fatal issues," adds Kalsi.

Frostbite is also a major risk in the bitter cold.

"This is where icicles in your tissue start to form and attack your cells," says Kalsi.

Frostbite symptoms include skin turning red blue or grey, pain, numbness and stiffness.

If you do suspect frostbite, warm the affected area by putting it next to warmer skin and immerse your skin in lukewarm water.

Never rub the affected area and if skin is blistering, seek prompt medical attention.

And always bundle up. Wear multiple layers and ensure the outer later is windproof.