Humans are good at smelling cheese thanks to special smell receptors

Smell that? If it’s cheesy, sweaty or sweet, you might be more likely to sense an odour. Humans have evolved many more smell receptors for these scents than anything else, probably to help us choose which foods to eat.

Luis Saraiva at Sidra Medicine in Doha, Qatar, and his colleagues looked at smell receptors in mice and people. They started by analysing the small patch of neurons that contain smell receptors. This area is about 2.5 square centimetres in humans, and sits in between the eyes at the top of the nasal cavity.

To find out which smell receptors mice and people have, the team extracted mRNA from each of the samples. This molecule plays a key role in allowing genes to make proteins, so the team used mRNA levels to tell them which genes in each sample were “switched on”, as well as their relative abundance.

Both species have more receptors for odours that smell like rancid milk or cheese, sulphur or sweat, or are particularly sweet or spicy-smelling, like vanilla or clove than for other smells. This may mean that we are more sensitive to these scents, although we can’t say for sure yet.

In humans, these smells are important for helping us make decisions about which foods to eat, and for distinguishing between what’s ripe and what’s rotten, says Saraiva. But in mice, the chemicals act as pheromones – chemicals that can change their behaviour, such as those that attract mates.

Some of the chemicals that humans have lots of smell receptors for are also found in bodily fluids like breastmilk and vaginal fluid. These act as pheromones in other primates, but there is no evidence that they do in humans, says Saraiva.