An Emotional Time Machine: How Our Sense of Smell Can Unlock Childhood Memories

What is your favorite smell? This question may seem banal, but think carefully, because your answer will say something about who you are. Our most meaningful smells evoke intimate feelings, similar to how we are affected by music or art. It is almost impossible to talk about your favorite smell without getting personal. The smell of our partner or our children evokes feelings that are difficult to describe in words. A friend who recently became a father described the smell of his child as making him giddy with love. For dog lovers, the smell of the family dog is often high on the list of favorite smells.

These feelings are shaped by our memories and experiences. Researchers have shown that people often think other people’s pets smell bad, but not their own pets. New parents have the same attitude toward dirty diapers—it doesn’t smell as bad if it comes from your own child. These smells have a special meaning for us, and the emotions they evoke are due to olfactory memory—smelling enables us to remember events and emotions, and associate them with each other. This is what makes smells so deeply personal.

Like few other impressions, smells can take us back to childhood and bring back old memories. It is an “emotional time machine,” according to olfactory memory researcher and my long-term collaborator Maria Larsson. Most of us have one or more smells that evoke childhood memories. The smell of lily of the valley, for example, can remind us of the bouquet of flowers we picked that special last summer before starting school. This peculiar phenomenon is usually associated with the writer Marcel Proust, who, in the first volume of Remembrance of Things Past, dips a madeleine cake in lime-blossom tea. It is a very special novel, not only because of its length, seven huge volumes, but because of the winding, associative style with which Proust demands the reader’s attention. The focus is on sensory impressions; it is the senses that evoke feelings, thoughts and reflections. And which bring back memories of childhood.

Proust begins by describing how for a long time the protagonist could not remember more than the most basic and general aspects of his childhood in Combray—the name of the village in which the book’s protagonist grew up. The familiar surroundings were hidden in “unchanging evening light.” Proust writes of the past as an elusive world that we cannot summon with our minds. But everything changed with the madeleine cake his mother served him with tea on a cold winter day…No sooner had the warm liquid mixed with the crumbs touched my palate than a shiver ran through me and I stopped, intent upon the extraordinary thing that was happening to me.

This is followed by an intense passage about how the memories begin to haunt him, announcing their presence for brief moments and then sinking back into the darkness of oblivion. He tries intensely, seemingly at the cost of his life, to get hold of the elusive memories. Finally, with the help of smells and tastes, he manages to unlock the treasure chest of memory. In Proust’s hands, sensations and associations become great literature.

“The sight of the little madeleine cake had recalled nothing to my mind before I had tasted it; perhaps because I had so often seen such things in the meantime, without tasting them, on the trays of pastry cooks’ windows, that their image had dissociated itself from those Combray days to take its place among others more recent. But when from a long-distant past nothing subsists, after the people are dead, after the things are broken and scattered, taste and smell alone; more fragile but more enduring, more immaterial, more persistent, more faithful, remain poised a long time, like souls, remembering, waiting, hoping, amid the ruins of all the rest; and bear unflinchingly in the tiny and almost impalpable drop of their essence, the vast structure of recollection…And as in the game wherein the Japanese amuse themselves by filling a porcelain bowl with water and steeping in it little pieces of paper which until then are without character or form, but, the moment they become wet, stretch and twist and take on colour and distinctive shape, become flowers or houses or people, solid and recognizable, so in that moment all the flowers in our garden and in M. Swann’s park, and the water lilies on the Vivonne and the good folk of the village and their little dwellings and the parish church and the whole of Combray and its surroundings, taking shape and solidity, sprang into being, town and gardens alike, from my cup of tea.”

For quite some time, Proust was alone in exploring the connections between olfaction and memory. When researchers ask their study participants to write down their notable memories, they tend to focus on experiences that they can visualize and that have had a significant impact on their lives: a childhood friend, an early romance or perhaps negative experiences of victimization and bullying. The more vivid the memories, the more activity they elicit in the brain’s visual cortex. When studying memory in this way, smells are rarely included. However, another memory method began to be used in the 1970s, which paved the way for the study of olfactory memories.

This method used a list of words presented to all participants as memory cues: library, clock, factory, street and so on. The words, researchers would later realize, could easily be exchanged for different sensory impressions, enabling a comparison of how these impressions triggered different types of memories. Among the first to use this method to study olfactory memories were Maria Larsson and Johan Willander, who invited hundreds of elderly people to their research laboratory at Stockholm University. They asked participants to describe the memories triggered by words, sounds, images—and smells. The results were surprising.

Smell memories were dramatically different from memories triggered by other cues. It was known that words trigger memories from two specific periods of life. One period is the last few years. A third of all memories evoked come from experiences in recent years, which is not surprising as they are particularly fresh in our minds. However, we tend to forget events that are farther back in time, when more has been lost to oblivion. The most interesting period is therefore not the one that is closest in time, but the second period, where many memories are evoked despite being far in the past: adolescence and early adulthood. Here we see a curious “bump” in the memory curve that extends roughly from age eleven to thirty and peaks at about age twenty. This period of time sees an unusually high accumulation of memories, despite being sandwiched between two other periods that we don’t remember very well at all, childhood and, if we are old enough to have passed it, middle age.

The experiences of childhood are believed to be inaccessible to us because our brains are simply too immature at that time to create lasting memories of our experiences. Our knowledge of the world, our identity, self-image and language skills help us remember our lives. But in childhood, these skills are far from fully developed, and as a result, childhood experiences are often not recorded in memory. So researchers have developed theories about the “bump,” the accumulation of memories of our experiences during adolescence and early adulthood. Some argue that it occurs at this time because the brain’s memory capabilities are at their best.

Others argue that it is a particularly eventful time of life that includes the entry into adulthood, where crucial life choices are made and where one’s future life begins to take shape. Perhaps both theories are true. But the strange thing about olfactory memories is that they do not come from the same time period as the other memories. The olfactory bump appears already at the age of six to ten years.

It is now well established that smells have a unique capacity to evoke memories of childhood. But that is not all. Olfactory memories are also different in other ways. They evoke a sense of “going back in time” in a way that no other sensory experience does. Smells can make you relive the time you helped your grandfather tar the rowing boat, the time you stepped out of the airplane on your first vacation to the Mediterranean or the wedding where you got to be a bridesmaid with your own bouquet of flowers. You remember the details, relive the moods. Smell memories are also more emotional than other memories. But why do smells have this property?

It is still something of a mystery, hidden in the twists and turns of our brain. And what makes it even stranger is that our memory for smells is not really very impressive in itself. When my colleagues and I examine the memories of different experiences under controlled conditions, we consistently find that our participants are much better at remembering images, words or sounds than smells. But even so, some of the smells that the brain stores are retained, and sometimes we carry them with us throughout our lives. They are more faithful and enduring, as Proust would have said. One reason for this could be that the different sensory impressions activate different brain areas, thereby engaging different psychological memory processes. In one experiment, participants smelled smells and listened to words that evoked childhood memories, while their brain activity was recorded.

The results showed that both the smells and the words triggered activity in similar areas associated with memories, emotions and visual impressions—a sign that the cues triggered stored memories that participants could “see” in their minds. But it was only the words that also evoked strong activity in the frontal lobe, where language and abstract thinking reside. The smell memories did not. One hypothesis is, therefore, that words can trigger more abstract thinking. With words as clues to memory, we can search our memory bank in a more systematic but perhaps also more impersonal way. Words can help us find more memories. But for smells, this strategic option does not exist—smells can only bring to life the personal experiences, those that have a clear sense of personal presence and emotional charge. My own research supports this interpretation.

My colleagues and I have studied the olfactory brain’s connection to the brain’s memory center, and compared the strength of this connection to hearing, sight and touch. This is measured by looking at how the activity in the areas increases and decreases; if two areas “oscillate” in sync with each other, it can be interpreted as close communication. And it turns out that the olfactory brain, more than the other senses, oscillates in time with the brain’s memory center. But the sense of smell’s direct contact with the memory center probably comes at a cost. Smell does not have the same ability as do words to inspire abstract thought and the creation of strategies for memory retrieval. This leads to fewer but more concrete, intense and emotional memories being evoked by smells.

But a mystery remains. Why do the smells evoke such old memories? So far there is no definitive answer to that question. But my research with colleagues at KTH Royal Institute of Technology in Stockholm provides a possible explanation. We already know that the sense of smell develops very early in life. By mid-pregnancy, the fetus can smell the food the mother eats. French researchers have been able to demonstrate this using aniseed pastilles, which they allowed pregnant women to eat in large quantities. When the babies are born, they seem to be particularly interested in the smell of anise—they turn their heads toward the smell of anise in the cradle!

The smells a baby is exposed to in the womb can actually influence what food they will be interested in in the future, so strong and so early are our first olfactory memories. And we believe that this early development of the sense of smell can explain the memories that Proust described so vividly. Our calculations show that if the olfactory brain “matures” earlier in life than other brain systems, this can actually explain the childhood memories. Nerve cells become less and less receptive to new memories as they get older. This means that the malleability of the sense of smell may be greatest in childhood. Later, when the malleability has decreased, the childhood smells that we have memorized are protected because the neurons are no longer as malleable—but this comes at the cost of the smells we encounter in adulthood not being as easily stored.

And this is exactly what we find in our memory experiments: adults often have difficulty remembering new smells. Other sensory systems mature later than the sense of smell, which may explain why, for example, visual and auditory memory storage is strongest in adolescence and early adulthood, but smell memory is not. So perhaps we are on the way to solving the mystery.

Memories are the most important building blocks of our lived experiences. What we remember becomes part of us, of our identity and self-image. Memories allow us to develop, both as individuals and as part of society. But memories are not just a mechanical recall of past experiences. When we remember, we also create a story about ourselves. Your olfactory memories are unique, but they probably reflect something that is still important to you today. I am often struck by the way smells are used in autobiographies.

Despite the fact that smells are usually so difficult to describe, skilled writers can use them to engage the reader emotionally. Describing smells, like few other impressions, can bring a presence to the text, giving it a personal appeal. Märta Tikkanen’s Love Story of the Century is about a destructive marriage with a drunken, abusive husband. She describes how the smells of cigarettes, sherry and stale beer take over the family’s apartment and permeate their sad existence. Other descriptions of smells are less graphic, but still reveal strong emotions. Eric Rosén writes about his alcohol-dependent father in the book Jag ångrar av hela mitt hjärta det där jag kanske gjort. Rosén describes without frills the smell of spoiled food from the refrigerator that has been turned off because his father has not paid the electricity bill. No graphic descriptions are needed to make the reader feel sad and angry that children have to grow up like that—the smell explains everything.

Literary descriptions of smell can also tell more uplifting stories. The Swedish physician and professor Hans Rosling’s autobiography How I Learned to Understand the World opens with not one but two powerful olfactory memories. One is the memory of coffee-smelling coins that Rosling’s father brought home from work at the Lindvalls coffee roastery in Uppsala. The workers who packed the coffee in South America put the coins in as a greeting to their colleagues on the other side of the world, and Rosling’s father told his son about the distant countries where the coins came from. This sparked Hans Rosling’s interest in the world and global developments. The second smell that opens Rosling’s autobiography is less pleasant—the smell of sewage. He remembers the smell from his childhood, when the sewers were still open and ready to spread disease.

Sewers were covered in Sweden in the 1940s (an important part of modernization), but Rosling describes how he often visits countries that do not yet have a functioning sewer system. It brings back memories of his childhood, but for the eternal optimist Rosling, the smell of sewage also evokes a sense of hope, because more and more countries are now reaching a level of development where the spread of infection and child mortality can be minimized.

Exploiting Proustian olfactory memories—especially nostalgic ones—is every marketing expert’s dream. Anyone who can unlock the door to our childhood with a simple smell has a world to gain.

But olfactory memories are unique to us. No two memory portals are the same. Each person must therefore have their own olfactory key. And what unlocks each portal can smell like pretty much anything. On April 1, 2019, the Swedish Scouts launched their own fragrance, Go Camping, inspired by camps, summer, outdoors and nature: “A deep base note of campfire is tastefully combined with middle notes such as pine and leather, and top notes of dewy summer meadow…and damp wool socks.” An April Fool’s joke, of course, but surely anyone who has been a scout, or had similar nature experiences, can also enjoy the smells that make others wrinkle their noses.

Now I want to ask you to do a little experiment. Ask someone to take three items out of your pantry or refrigerator and hold them under your nose. Close your eyes, and try to name the smells they contain without any other clues. How did it go? You probably got one of the three right. This is exactly what olfactory researchers discover when they ask their participants to name everyday smells. Most people are amazed at how difficult it is to recognize familiar spices such as thyme, allspice or basil. They often say that the smell is very familiar, and they can often provide some information about the smell. That it is a spice, a fruit, a flower. But the exact source of the smell often remains inaccessible to us. If we have such an excellent sense of smell, shouldn’t we be better at recognizing and describing smells?

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From The Forgotten Sense: The New Science of Smell—And the Extraordinary Power of the Nose by Jonas Olofsson. Copyright © 2025. Available from Mariner Books, an imprint of HarperCollins Publishers.