Minnesota doctors want people to be on alert for frostbite and know its symptoms as painfully cold temperatures pierce the area.

"Obviously, the key is to avoid exposure to extreme cold temperatures," Dr. Ryan Fey, at Hennepin County Medical Center's Burn Center, stressed. "That means staying indoors when it's cold, and if you have to be outdoors for any length of time, making sure you dress appropriately to stay warm — even if it's just a run to the mailbox or from your house to your car."

Bitter cold will keep Minnesota in the deep freeze most of this week, with temperatures stuck in the single digits on Tuesday and below zero on Wednesday. Although temperatures will push into the teens on Thursday, they'll plummet back into single digits for the weekend.

Last winter, doctors at HCMC's Burn Center treated 200 patients with frostbite injuries. That is a record year compared to 25 patients in an average year.

HCMC lists the stages and symptoms of frostbite by degree:

First degree: A mild form of frostbite in which your skin turns red and feels really cold.

Second degree: In this stage the reddened skin will turn white or very pale. Upon warming, blisters may appear. This results in some tissue and nerve damage.

Third degree: Affecting all layers of the skin, the area will turn black and hard as tissue dies.

Mayo Clinic doctors say a prickling feeling or numbness can be an indication that your skin has been affected by the cold. Mayo Clinic emergency medicine specialist Dr. David Nestler compares frostbite to burns.

"If there was too much fire exposure, that could damage the fingers to where they couldn't survive. Cold can do the exact same thing, "Dr. Nestler said. "It's the opposite extreme with the same effect, which is tissue that is nonfunctioning."

If you or someone you know shows any severe signs of frostbite, doctors say it is best to get them medical attention immediately.

"Rewarming should be done as quickly as possible in a 40-degree water bath, "Dr. Fey advised. "You want to rapidly and definitively rewarm the extremity once — and only once — to avoid the freeze/thaw cycling which magnifies the degree of injury."

Vineeta Sawkar — Twitter: @vsawkar