It's a phrase coined by Shakespeare in his play Cymbeline. As far as I know, it never had a basis in science but was a common belief.
During the Cold War, with the possibility of fighting in the USSR, the US Army conducted experiments with soldiers doing extended bivouacs outside in cold weather to see whether there was increased likelihood of sickness. They couldn't find any evidence that it did.
During the Cold War, with the possibility of fighting in the USSR, the US Army conducted experiments with soldiers doing extended bivouacs outside in cold weather to see whether there was increased likelihood of sickness. They couldn't find any evidence that it did.