Researchers collected data for a closer look at the science behind human smell perception. (Krakenimages.com/Shutterstock)

JENA, Germany — Why does freshly cut grass smell like summer? What makes a bakery’s aroma so universally appealing? And why do some smells trigger vivid memories while others repulse us instantly? Despite being one of our most primal senses, our understanding of how humans perceive smell remains surprisingly limited.

A new study published in Scientific Data has taken a major step toward decoding this mysterious sense by creating an extremely thorough dataset of human odor perception. Researchers from German universities have collected detailed smell descriptions and ratings of 74 different chemical odors from over 1,200 people, providing an unprecedented map of how average people, not perfume experts, experience and describe scents.

The Mystery of Smell

For decades, scientists have struggled to answer a seemingly simple question: why does an odor smell the way it does? While we’ve identified roughly 400 smell receptor genes that somehow recognize over a million different scents, the connection between a molecule’s chemical structure and its perceived smell remains largely mysterious.

“The chemical structure of everything in our environment that we can smell is generally very complex. We are usually unable to say exactly what odor the individual chemical components emit, as the individual substances dock onto different receptors in the nose depending on their composition. For example, we don’t know how a certain amount of carbon atoms smells,” says study author Antonie Bierling from the Institute of Psychology at the University of Jena, in a statement.

Most existing smell databases come from trained perfumers or industry experts using predefined labels, making them less representative of how ordinary people perceive odors. This new research addresses this gap by collecting perceptions from everyday people, offering a more authentic picture of the human smell experience.

The research team recruited 1,227 participants, primarily young adults, who smelled and described a diverse array of 74 mono-molecular odors (simple chemical compounds with just one type of molecule). Since having each person smell all 74 odors would lead to sensory fatigue, participants were divided into nine groups, with each group testing 10 odors. Two “anchor” odors appeared in all groups for comparison, while the other eight were unique to each group.

Participants first wrote down their own descriptions of each scent, then rated them on eight characteristics: pleasantness, intensity, familiarity, warmth, coldness, edibility, disgust, and irritation. They also indicated whether each smell could be described by 16 qualitative labels like “sweet,” “chemical,” “floral,” or “musky.”

Beyond just collecting odor perceptions, researchers gathered data on participants’ demographic backgrounds, personality traits, and the role smell plays in their daily lives. This extensive dataset offers a foundation for investigating how factors like gender, age, and personality influence smell perception.

What They Discovered

The study backed up what past research has found but also brought some fresh insights to the table. Like expert studies before it, participants’ ratings followed clear patterns, especially when it came to how pleasant certain smells were. But at the same time, there were big differences in how people described and experienced the same odors.

When researchers compared their results to a 2016 study on everyday smell perception, they found strong similarities in how people ranked odors for pleasantness, familiarity, edibility, and intensity. This suggests that, despite our personal differences, there are some universal patterns in how humans perceive scents.

One of the most interesting takeaways is that our sense of smell is surprisingly stable over time. When participants were tested a week later, their ratings and descriptions were remarkably consistent, especially for how pleasant, edible, or disgusting an odor seemed.

Beyond the Lab: Real-World Applications

This research isn’t just academic curiosity. Understanding the relationship between molecular structure and smell perception has practical applications ranging from creating more effective artificial flavors to developing digital smell technologies. It might even help clinicians better diagnose and treat smell disorders, which affect millions worldwide and can significantly impact quality of life.

“Our smartphone, for example, can recognize our face or our voice – but when it comes to digital smelling, developers are still coming up against fundamental limits,” explains Alexander Croy, a physicist from the Institute of Physical Chemistry at the University of Jena. “With the help of such research results, however, we are already getting closer to the electronic nose and may even be able to identify our own body odor at some point.”

Building a Language of Smells

One of the study’s most interesting aspects is how it captures the subjective language people use to describe smells. The researchers standardized and translated participants’ free-form descriptions, creating a valuable linguistic map of smell perception. For example, they tracked how often people used terms like “lemon,” “chemical,” or “sweet” to describe each odor.

The international research team purposely selected a diverse array of molecular compounds that span the “chemical space” of possible odors. They carefully controlled the concentration of each substance so that all smells would have roughly similar intensity, allowing for more accurate comparisons.

Smell is perhaps our most emotional sense. A scent can instantly transport us to childhood memories or trigger strong feelings of attraction or repulsion. This powerful connection to emotion and memory makes smell unique among our senses and particularly difficult to study objectively.

In a move toward practical applications, the researchers are making their results available to the public through an app. This allows anyone to explore the dataset and potentially contribute to our collective understanding of smell perception.

The Jena and Dresden research team isn’t stopping with this study. As part of a project called “SMELLODI” (Smart Electronic Olfaction for Body Odour Diagnostics), they’ve collaborated with international colleagues to develop another dataset focused specifically on body odors.

“We know that certain diseases have an impact on body odor. It can, therefore, be very helpful in recognizing and diagnosing illnesses to record it in detail,” says Bierling.

Creating a Dictionary of Body Odors

This resulted in a cataloged dictionary of bodily odor descriptions in 13 languages, revealing interesting patterns across cultures. For example, participants consistently described armpit odor as sweaty, sour, and stinky; bad breath was characterized as either fresh or stinky; and foot odor was commonly described as cheesy. This second database is also accessible through an app.

The next time you catch a whiff of something that instantly triggers a memory or emotion, remember that your brain is performing an incredible feat of chemical recognition. Thanks to research like this, we’re getting closer to understanding exactly how that magic happens, one molecule at a time.