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Sweating like a pig

The expression "sweating like a pig" doesn't really make sense if you know anything about pigs. Like the fact that they can't sweat.

A graduate student at the University of California was having a little dispute with his girlfriend. It seems she had started massage school and came home with some newly acquired information from a classmate. She was told that she should stop eating pork because pigs have no sweat glands and thus don’t sweat out toxins. Presumably then pork is unsafe to eat because of the toxins it harbours. There is some truth here. Pigs really don’t sweat. Not much anyway. As far as the rest goes, pure bunk. Sweating does not remove toxins, its purpose is to cool the body through evaporation. Perspiration is mostly liquid water, ready to change into water vapour by the input of heat. The heat needed for evaporation is drawn from the skin, cooling the body. 

True, sweat does contain small amounts of minerals and traces of organic compounds, some of which are responsible for smells. Bacteria on the surface of the skin convert fats in sweat to odiferous compounds such as butyric acid. And there are also very small amounts of compounds like androstenol or androstadienone that may have some pheromonal activity. But any “toxins” would be present in vanishingly small amounts for the simple reason that the sweat glands are not connected to the bloodstream. And that is where toxins lurk. Yes, we do harbour them. Sampling of blood or urine reveals traces of hundreds of compounds that originate from the likes of cosmetics, cleaning agents, medications, car exhaust, flowers, cat litter, wood stoves and food. But our liver and kidneys do a great job of getting rid of most of these. Sweat glands need not apply for employment. They are unequipped to help.

But of course a lack of understanding of toxicology and physiology does not deter the promoters of various quack detoxication regimens. There are foot baths and patches that supposedly suck out toxins. Exactly what these toxins are is never mentioned, nor is any evidence of their removal provided.  And then there are the infrared saunas and sweat lodges that claim to detoxify through heavy sweating to carry toxins out of the body. Infrared saunas use infrared light that penetrates the body and warms up tissues from within instead of heating the body from the outside as in the case of a regular sauna. The claim is that this causes “toxins” to be released more efficiently because the infrared light penetrates deeply into the body. There is zero evidence for this.

Actually, when sweating is carried to an extreme it can cause dehydration and impair the work of the kidneys. This is what happened when three people died in an Arizona sweat lodge ceremony organized by self-help guru James Arthur Ray, who was eventually sentenced to two years in prison for felony negligent homicide. Ray charged participants up to $10,000 for a weekend retreat where they were to learn about his philosophy, described as a mix of spirituality and quantum physics. They came to “better themselves and detox their bodies.” Sad. The belief in this kind of cleansing by sweating is as ridiculous as the belief that pigs should not be eaten because they’re full of toxins since they can’t sweat. 

But if pigs can’t sweat, why do we have the expression “sweat like a pig?” The term is actually derived from the iron smelting process in which hot iron poured on sand cools and solidifies with the pieces resembling a sow and piglets. Hence "pig iron". As the iron cools, the surrounding air reaches its dew point, and beads of moisture form on the surface of the "pigs". "Sweating like a pig" indicates that the "pig" (ie iron) has cooled enough to be safely handled. And that's a "pig" you wouldn't want to eat.


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