2778: Sweat Like a Pig Jul 29, 2024

Pigs, famously, do not sweat, which is why they have to roll in mud in order to cool themselves down; water is a far better conductor of heat than air. So out of all animals, how did the phrase “to sweat like a pig” develop? Some phrases are hard to pin down, because some of the phrase was lost, and now it sounds strange out of context, such as, “happy as a clam [at high tide]”, or sometimes the connotations of those words change, as in, “kick the bucket”. In this case, it is closer to the latter reason.

This name comes not from pigs the animals, but from pig-iron, a name for an intermediate stage of iron in the iron smelting process. Pig-iron, which is crude iron cast into ingots, got its name from the fact that lots of ingots would be poured at once from a central channel, respectively referred to the piglets and sows. 

Once the iron is cooling, as with any cast iron, water droplets form around the metal like sweat. In lots of cases, metal is referred to as sweating, not just with iron but also steel and copper etc., even though much like real pigs, pig-irons don’t sweat either.