Matthew Cobb

Smell—or olfaction, to give it its scientific name—is probably the oldest sense. Organisms were able to detect chemicals in their environment and directly respond to them long before they could see or feel, although the mechanisms involved have long since changed profoundly.

But odours resist verbal categorization.

The olfactory world is far richer than we imagine. Odours also come in different concentrations, and our feelings about an odour change with its intensity

Myth 1: You smell with your nose. Although we can indeed smell by inhaling through our nostrils, we detect odours using neurons that are directly connected to the brain, which dangle down through the base of the skull, at about eye level (). Really, you are smelling with your brain

While it is generally the case that your sense of smell might be diminished if you are aged, or if you smoke, and you will generally be better at smelling if you are female (overall, women have a more acute sense of smell than men), in reality we all have an atomic nose

In 2014 researchers in the laboratory of my good friend Leslie Vosshall at Rockefeller University tried to estimate how many smells we might be able to tell apart, based on mixtures of molecules. They came up with the astonishing figure of over a trillion. Although this mathematical model has been challenged, it seems probable that there is no real limit to the number of odours we can detect. The same will apply to many other animals

Your sense of smell and your sense of taste are intimately connected.

our perception of flavour is a mixture of the simple world of taste and the rich, multiple dimensions of smell. In many languages, flavour is colloquially called ‘taste’ even though smell may be the dominant sense giving flavour its subtlety.

These biological effects are melded with cultural norms over which smells are and are not socially acceptable. Over recent decades in the West, we have become very conscious of avoiding personal odours, and spend a great deal of money and effort trying to ensure we do not smell of sweat or other odours that are perceived as unpleasant. In other times and other societies, different rules have applied

Smell has even been used to tell the time—from the 11th century onwards, Chinese temples used aroma clocks, containing powdered incense that burned at a particular rate, to release different scents at different times