Caution: Low-temperature burns from foot warmers

Beware of cold burns.

The low-temperature burn I've only heard about... to me...

I turn on the foot heater because the office is cold.

While washing, I noticed that the calf area is mottled, looking like a bluish bruise.

Wow... I was wondering what it was, and it turns out this is a cold burn...

It doesn't form blisters or anything, but it takes a long time to heal.