Why do people find certain smells appealing

Senses: How fragrances manipulate us

Hanns Hatt's hair stands up at the smell of printer's ink. Every time he gets his nose at the scent, he shudders. Because he reminds the renowned cell physiologist and odor researcher at the Ruhr-Universit├Ąt Bochum of his school days, which at least was a bit behind: "I hated schoolwork. That's why I still have an aversion to the smell of freshly printed paper."

Fragrances can therefore evoke intense sensations in us even after decades: Our brain stores the olfactory sensory impression and, as soon as a certain fragrance snakes back into our noses, lets us revive long-forgotten memories. Whether something smells good or bad depends solely on the situation in which we smelled it for the first time. "Everyone has their own fragrance preferences," says Hanns Hatt, "most of them are shaped or brought up by their own experiences, for example by their parents." We save a smell that we have experienced in a beautiful situation more quickly as a pleasant fragrance than one that reminds us of an unpleasant experience. The scent of oranges, for example, is perceived by most people as having a good smell, because oranges are often associated with Christmas.

This article is included in Spectrum - The Week, 21/2015

Smell already in the womb

Even unborn babies can smell from the 28th week of pregnancy and store the mother's olfactory preferences as positive. Humans have "only" about 30 million olfactory cells, while dogs have about 300 million. Each and every one of our olfactory cells is a specialist and only reacts to certain scents. The specialization, however, is broad: a cell can recognize up to 20 different odor molecules, which, however, must have a basic similarity in their chemical structure. With 350 different receptors, we can perceive and assign a corresponding number of scents - for comparison: rats and dogs have 1000 different receptors. Nevertheless, we humans can (theoretically) differentiate up to a trillion scents, discovered researchers led by Andreas Keller from Rockefeller University in New York: Our sense of smell works more finely than long thought.

For example, a cell that specializes in the smell of vanilla only makes receptors for vanilla. If they are activated by the scent of a vanilla pod, for example, the cell sends electrical impulses via its nerve process to the olfactory brain. From there the impulse is transported further into the limbic system - an area in our brain that is responsible for our feelings and moods; on the other hand in the hippocampus, our memory and memory center. The other sensory perceptions such as sight and hearing also occur here, but with the difference that they have mostly passed the thalamus beforehand - the gateway to consciousness. Smell is a sensory perception that can have a direct effect on our emotional life.

"Our well-being is enormously influenced by smells," says Hatt, "everyone has to find their own feel-good scent first." And that, too, only works through personal experience and can be trained: If I am happy and smell a scent, over time it becomes imprinted on my olfactory memory. Little by little, the effect will reverse and the scent will make you feel happy.

With fragrances against cancer

Fragrances can also have positive effects on the body through breathing, if the fragrance is absorbed into the blood through the lungs. This can be done, for example, by applying scented oil to the skin or through food and the gastrointestinal tract. Certain fragrances can even have pharmacological effects. For example, linalool, an ingredient in lavender, or gardenia acetal have a similar effect on the body as promoting sleep as Valium.