Matched was inspired by the power of the human nose, millions of years of evolution, and my hope to make the world a better-smelling place.

Below is an extended tour of my research journey to understand the human sense of smell, the art of perfumery and food science, human genetics, and immunology.

The result is Matched - a company dedicated to helping you smell incredible.

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Scent in the Ancient World

The sense of smell has played an important role in human culture since ancient times. In Mesopotamia, Egypt, China, Greece, and Rome, scent was deeply intertwined with religion, medicine, and social interactions. In Mesopotamia, incense was burned during rituals to honor the gods, and the fragrant smoke was believed to have purifying powers that connected people to the divine. The ancient Egyptians, known for their intricate burial practices, used a variety of aromatic substances in the mummification process to both preserve the body and provide a pleasant fragrance for the afterlife. Frankincense and myrrh, two of the most famous resins used in ancient Egypt, were highly valued not only for their scent but also for their supposed medicinal properties.

In ancient China, herbs and aromatics were extensively used in traditional medicine to maintain health and treat illnesses. The concept of balancing the body's vital energy (qi) was fundamental to Chinese medicine, and scents were considered to help harmonize the body's energies. Aromatic herbs like sandalwood, camphor, and agarwood were used in both medical treatments and spiritual practices, highlighting the dual role of scent in physical and emotional well-being.

Greek and Roman cultures also placed significant importance on scent. The Greeks, influenced by Egyptian practices, used perfumes in religious ceremonies, as well as in personal grooming and social activities. Philosophers like Theophrastus studied the properties of various scents and their effects on mood and behavior, laying the groundwork for what would become the science of aromatherapy. The Romans, meanwhile, were known for their elaborate public baths, where the use of scented oils and perfumes was a sign of luxury and refinement. Roman society's appreciation of fragrance extended to their homes and public spaces, which were often perfumed to create a pleasing environment.

In all of these ancient cultures, scent was more than just a sensory experience – it was a symbol of status, a means of communication with the divine, and an essential part of healthcare and personal hygiene.

These ancient societies understood the importance of scent, just not its chemical and biological mechanisms.

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Olfactory Winter

From the mid-19th through late-20th century, the majority of scientists in the western world believed that humans possess a vastly poorer sense of smell compared to other mammals.

You might blame this on a 19th century anatomist Paul Broca, who suggested that the evolution of human free will necessitated a reduction in the size of the olfactory bulb, a part of the nervous system connecting olfactory receptors to other parts of the brain. He based this idea on the observation that humans have relatively large frontal cortexes, giving us a capacity for reason and language beyond other animals. From that observation he generalized that bigger must always mean better. Observing the relatively small size of the human olfactory bulb relative to total size of our brains, Broca reasoned that  smell must be of diminished importance. He made this claim with no direct evidence of human olfactory performance, however the belief managed to spread. You could also blame Charles Darwin for popularizing Broca's ideas. Darwin wrote disparagingly in his 1871 book, "The Descent of Man,"  that our sense of smell is"of extremely slight service even to savages.

In the following 150 years the myth of poor-smelling humans persisted, yet scientists still made tremendous progress toward understanding olfaction in other species. In the 1950s, Adolf Butenandt, a German chemist, was instrumental in identifying the first known pheromone in silkworm moths, called bombykol. This finding was published in 1959 and marked the beginning of understanding chemical communication in animals. The study showed that female silkworms emitted bombykol to attract males, illustrating the role of chemical signals in mating behavior.

Further discoveries in the 1970s and 1980s highlighted the role of sociochemicals in a wide range of animal behaviors. Researchers such as Peter Karlson and Martin Lücher expanded the understanding of pheromones in ants, demonstrating how these chemicals were used to convey information about kinship, species identity, and trail marking. Their work emphasized the importance of pheromones in maintaining social order and facilitating group behaviors within colonies.

In 1979, Richard E. Brown published his work on the role of chemical signals in rodents, showing how pheromones mediated dominance status, mating status, and territorial marking. His research highlighted that mice and rats used urinary pheromones to signal individual identity and reproductive state, adding to the understanding of how animals use chemical cues to navigate their social environments.

The role of alarm pheromones was brought to light by John H. Law and Richard W. Regnier in 1971, who discovered that certain insects, such as ants and bees, released chemicals to warn others of potential danger. This discovery emphasized the complexity of sociochemicals communication and how it could convey emotional states such as fear and alertness to other members of the group.

Scientists' understanding of the anatomy in other animals also contributed to the believe that these effects wouldn't be relevant in humans. In particular, many of the sociochemicals in mammals were found to be detected by a special organ called the vomeronasal organ, or Jacobson's organ, after Ludwig Jacobson, a Danish surgeon, who studied it extensively in 1813. This organ appears in most mammals, as well as a handful of reptiles and amphibians. Ironically, it was first discovered in humans, where it seems to have no impact on perception conscious or otherwise. Due to the lack of a functioning vomeronasal unit, it was logically assumed that humans would have no way of detecting pheromones or other sociochemicals.

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Sociochemicals in Humans

The myth of poor human olfaction

We can detect certain molecules even better than dogs, who have roughly 50x our number olfactory receptors.

We can also detect odors that change in very short timespans, less than 60ms apart.

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Humans also have a complex smell-based communication system of our own. For example, we can smell each others' age, otherwise known as "old person smell." There are of course cleaning and cosmetic products that contribute to the smell of retirement homes, but indeed some of that smell is purely biological. One well known contributor is a single molecule called 2-nonenal, a nine-carbon unsaturated aldehyde. This molecule is a natural byproduct of metabolism that tends to increase in production as you get older. It's completely harmless, but contributes to a faint waxy, musty, grassy smell to the skin.

Another example is fear sweat, which contains memorably named "fearamone" molecules (Note: human pheromones, as formally defined, have yet to be discovered. More on that later). In studies where participants were asked to evaluate the pleasantness of various t-shirts that had been worn for a few hours, they could reliably distinguish between the shirts worn during a fun athletic activity versus a stress-inducing activity like taking a test. Surprise! – people smell better when they're not stressed out.

Those two examples are far from the whole the list. We can also smell aspects of each other's personality, kin relationships, hormonal reproductive status, individual identity, and more. The ability to identify members of one's family (kin) through odor is a particularly strong ability, likely relevant to historically to mother-child bonding, as well as inbreeding prevention. This list is ever growing as research increases in the previously neglected area of human olfaction and social behavior.

In particular, the effect that inspired Matched comes from the deep connection between our immune systems and perceptions of smell. In 1995, through their now famous t-shirt experiment, Claus Wedekind et al. found that women can reliably smell aspects of male immune systems through body odor. They demonstrated this by presenting women with T-shirts worn by men for a few hours and asking them to rate the pleasantness of the smell. It turned out that women generally preferred the smells of men who had dissimilar HLA types to themselves, which is there HLA is the name for the genes we all have that program our innate immune system.

This result makes sense from evolutionary standpoint. HLA genes give each of us a level of immunological uniqueness, so the more genetic diversity in the population the less likely it is that a single pathogen can wipe out the entire species. There may be other mechanisms in play, but having a way to tell when someone's immune system is too similar to your own via body odor likely had an effect in creating the incredible diversity of HLA genes we see today. In humans, there are over 40,000 known alleles for the combined HLA class I and II genes. With 9 primary genes in that complex, the theoretical number of possible combinations an individual might possess is literally astronomical in scale. In reality, the total number of measured unique genotypes is significantly smaller (due to "linkage disequilibrium," or correlations between alleles), yet HLA remains by far the highest-variation set of genes in humans.

Although the theory behind Wedekind's finding is strong, there are few caveats in practice. For one, follow up studies found that that it's much harder to measure this effect in the other direction, i.e. with men perceiving women's odor. That isn't too surprising since women, in both evolutionary and common terms, are the "choosier" sex. Due to their higher guaranteed risk and commitment in the production of offspring, women have evolved a stronger set of tools than men to evaluate the fitness of potential partners, including by smell. A small, but related aside – women not only have more perceptive senses of smell, but consistently underrate smell as a factor in evaluating potential partners. In their 2024 study, Eastwick et al, found that "smelling good" as a criterion for women assessing male partners had the largest gap in importance between what women reported on surveys versus what actually determined the outcomes of their relationships. So in terms of detecting HLA compatibility, it's expected that women would be more sensitive than men. Furthermore we lack studies measuring this effect in gay, trans, or nonbinary individuals. We hope that other research institutions will conduct studies to understand how HLA influences these communities, or that we can conduct them at Matched at some point in the future. A final, slightly startling caveat is that later studies revealed that women taking hormonal contraceptives didn't prefer HLA-dissimilar men. In fact their preference was flipped. They actually preferred the smell of men who were more HLA-similar than average. There's at least one plausible evolutionary explanation for this: that women who are pregnant (or in a hormonally similar state to pregnancy due to use of hormonal birth control) were generally advantaged by surrounding themselves with family. This advantage may have resulted in an odor-driven preference for the company of family during pregnancy, mediated by HLA genes.

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Modern Fragrances, and Matched

Now for the big question – how does it work? We know there's a psychological effect and a reason to expect that effect, but what exactly is your nose smelling when it identifies someone with compatible HLA? 

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