Putrescine originates in putrefying and rotting flesh, and is quite literally, the smell of death. It is one of the breakdown products of some of the amino-acids found in animals, including humans. Although the molecule is a poisonous solid, as flesh decays the vapour pressure of the putrescine it contains becomes sufficiently large to allow its disgusting odour to be detected. It is usually accompanied by cadaverine (named after the cadavers that give rise to it), a poisonous syrupy liquid with an equally disgusting smell. Putrescine and cadaverine also contribute towards the smells of some living processes. Since they are both poisonous, the body normally excretes them in whatever way is quickest and most convenient. For example, the odour of bad breath and urine are 'enriched' by the presence of these molecules, as is the smell of semen, which also contains the related molecules spermine and spermidine.
