Our family of five eats essentially the same meals and lives in the same environment, yet our faeces have different and identifiable smells depending on the individual. This must be to do with whatever lives in our intestines. But what is it?
鈥� The characteristic odour of faeces is almost entirely due to the presence of minute quantities of aromatic nitrogen compounds, such as pyridines, pyrazines and indoles. These are present in varying proportions in the faeces of different individuals and constitute a sort of olfactory fingerprint.
As writer noted in The Song of Quoodle, the human nose is notoriously insensitive compared to most mammals.
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However, it is extremely sensitive to these particular compounds, enabling us to distinguish our own faeces, containing microflora to which our bodies are accustomed, from those of other people or animals, which may contain dangerous pathogens. This is why we find the smell of our own stools and flatulence relatively inoffensive, while those of other people are nauseating.
Interestingly, the perfumery industry takes advantage of this sensitivity, using trace amounts of these compounds to add piquancy to its products.
Roger Savidge, Shoreham-by-Sea, West Sussex, UK
This article appeared in print under the headline 鈥淒eposit account鈥�