Frostbite attacks within minutes and even tears turn to ice - life in the US isn't much fun right now, our US correspondent says.
Goodness me, it's cold in Chicago.
It was -29C (-20F) at the start of the day.
But with the windchill, it felt closer to -45C (-49F).
At these temperatures all sorts of nasty things happen to the human body.
Hypothermia sets in quickly if you aren't wearing the right gear.
Exposed skin succumbs to frostbite within minutes.
The moisture on the inside of your nose freezes.
Tears turn to ice.
Talking suddenly gets hard because your cheeks stop moving properly.
It's not very much fun.
Even the pigeons are struggling to keep warm. These ones were pictured huddling together in Buffalo
It will be a deeply unpleasant experience for the most needy people not just in Chicago but across the Mid West and later in the week, the North East.
It is worth remembering that as we gaze at beautiful pictures of a frozen landscape, or marvel as hot water spray turns to snow.
Stunning as it is, this cold is dangerous.