If you're a frequent reader of our blog, you'll be aware that sweat and urine are two different things — one is waste, and the other is meant to lubricate your body. But there's a third substance that might be misinterpreted, so we thought we should cover it too! Nobody wants to be in the (mis)lucky position of thinking they wet themselves because they were just sweating!
So here's a simple explanation of what sweat, urine, and perspiration are. You'll never call pee sweat again!
Sweat is a liquid that evaporates from the skin; it's typically salt water — three times saltier than seawater. When the body sweats, it releases heat to dissipate heat through evaporation. This energy is split into two parts:
1. The evaporation of sweat in the form of water vapour. This is a direct consequence of the large amount of work produced by muscles and is mediated by the nervous system, which sends signals to cause sweat to be released through the skin by the eccrine glands under the surface. This sweat evaporates from these glands and drips down onto the surfaces below.
2. Within the body, heat is dissipated by sweating through evaporation — just like the heat is (hopefully) dissipated through a radiator.
The skin produces sweat and moisture that evaporates on its own. It's essential to consider that this will vary from one person to another, for instance, in someone who has low hydration. In these cases, sweating can be pretty weak and inhibiting movement — which is why we recommend drinking plenty of water regularly when you're exercising, or your body temperature will be suppressed.
Urine contains water, salt, acids, urea and uric acid. It's what is leftover from the kidneys after blood has been filtered, and thus it consists of what your body doesn't want. Urine is produced from waste and excess water that isn't used by the rest of the body. It's a waste product of two processes:
1. Not using water or other substances through sweat or other means, which causes urine to be produced by the kidneys. 2. Burning calories through food intake or burning fat reserves will also cause urine to be produced by the kidneys.
Urine originates in a liquid form, but it thickens into a gel-like substance known as sediment (or 'sedimentation') when cooled down. This sediment is normal and expected if you're doing a lot of physical activity. Still, if your urine becomes impossible to get rid of, this can be a sign of metabolic problems or the buildup of crystals on the urinary tract.
So that's all great and dandy, but what are sweat and urine made up of? How can they be so different?
Sweat consists primarily of water (90% by volume), with 1-3% salt and 0.5-2% urea. Your sweat also contains glycerol, ammonia, lactic acid and other trace elements.
In contrast, urine consists primarily of water (95-96% by volume), with 2-7% salt, 1.8% urea and 0.3% uric acid. The remaining 2% of urine consists of a range of other nitrogenous compounds — including small amounts of creatinine, ammonia, organic acids and amino acids. This means that the components in one litre of sweat are different to those in one litre of urine!
What about other liquids such as sweat? Well... perspiration and sweat are the same things! They're both derived from the same process: sweating.
Perspiration is simply an archaic term for sweat because it's believed that perspiration originates from the Latin "perspire", which means "to breathe out great heat". However, sweat has also come to mean "an excessive amount of sweating" and can be used interchangeably with the more modern term sweat.