Why do sweat, urine and feces smell so bad?
1 Answer
They don't. We are trained - by evolution and "civilisation" - to dislike these smells.
Sweat is supposed to cool our bodies by excreting water. With it come a number of other products, that - after a while - will turn rancid through bacterial decay. Sweat, and I mean fresh sweat, also carries feromones, that tell our brains a lot about the sweating person (subconsciously of course).
Same goes for urine . Many animals use urine as territory markers, or as clues for being receptive for mating, or being pregnant. Doctors used to taste urine for sweetness (=diabetes), among others.
Faeces give an idea of the general health of an individual, and so does its smell.
The olphactory sense (=smell) is the oldest sense that organisms have. Even single-cell organisms can sense the difference between "food" and "danger".
We "know" that sweat, urine and faeces are not food. A dung beetle or a bluebottle might disagree with you about the faeces.
