Sense of smell plays a crucial role in our health — saving us from out-of-date food that looks fine to eat, even guiding our sexual behaviour through the subtle odour of pheromones (chemicals given off in sweat).
The perception of different odours is triggered when microscopic particles are breathed in and dissolve in mucous membranes in the nose.
Receptor cells in the nose then send signals via the olfactory nerve to receptors in the brain, to an area known as the olfactory bulb.
This also sends information to be processed further in other brain areas associated with such things as emotion, memory and learning — which is why some smells can remind us of certain memories or trigger specific feelings.
Women have more olfactory cells than men — up to 50 per cent, according to one study — which might explain why they consistently outperform men when distinguishing between different smells.
‘Our ability to smell is based on a complex process which can easily be disrupted at different stages,’ says Michael Papesch, an ear, nose and throat consultant surgeon at Whipps Cross University Hospital in London.
‘If any part of the chain is broken or damaged, then smell is not registered by the brain and all scents would be the same: sniffing a rose would be like sniffing cardboard.’
People who have lost their sense of smell completely — as a result of trauma or infection damaging olfactory receptors — can still perceive such strong scents as ammonia or menthol.
This is because these stimulate pain or temperature-sensitive nerves in a process known as chemesthesis, where signals bypass the olfactory bulb and are passed directly to the higher centre of the brain to trigger a sensation.
We may take it for granted, but a loss of sense of smell (hyposmia if it is partial, anosmia if total) can affect your health.