Professor Hummel, is there is a fragrance that most people like? A delight for every nose?
Thomas Hummel: Our preferences for fragrances can be both innate and learned. 20 years ago, for example, I found the smell of turmeric, a typical Indian spice used in curries, absolutely awful. But since then, I’ve been to India a few times and have some nice friends there. And in the meantime, I’ve come to find even curcuma quite acceptable! Our sense of smell functions to a large extent as a warning system. For example, if you drink half a bottle of whisky and then feel absolutely rotten for the next two days, you’ll no longer like the smell of whisky, an aversion that might last for the next five to ten years! Bad experiences of this kind lead to changes in our perception of a particular odour.
How does a generally weak sense of smell affect the enjoyment of food and drink?
Each dish has a different texture; it may be cold, warm or spicy. If the sense of smell slowly diminishes over the years, then these sensations predominate over the finer tastes. However, memories associated with odours become lost. Although they are still stored in the brain, they can no longer be recalled.
How many people are unable to smell properly and what are the reasons for this?
According to our data, about five percent of the population cannot smell anything. There are 15 percent whose sense of smell is weak and who can perceive odours only in high concentrations. The reason for this may be an accident or an infection. Or it may simply be old age – from 50 years onwards, the sense of smell often diminishes, and among 80-year-olds, one in three can no longer smell anything. We also have specific anosmia, a condition in which a person has normal olfaction and it is only certain odours that aren’t registered.
So this is like a sort of blindness or deafness of the nose? Can such people do anything about it?
They can try to train their perception of fragrances. The sense of smell can be improved by up to 50 percent if, over a six-month period, you spend a few seconds each day sniffing four different scents. These fragrances need to be quite distinct from each other. So not only the smell of flowers, but also something resinous, earthy or tingling – eucalyptus is a good example.
In the case of specific anosmia, olfactory receptors are capable of reconstituting themselves if you repeatedly expose yourself over a period of six months to fragrances that you have ceased to smell. We have observed this in the case of new parents. People who have previously been unaware of any particular odour emanating from a newborn child suddenly become sensitised to their scent and are able to tell different babies apart with their eyes closed, and even to know if they are girls or boys.