When body odor is described as “spicy” or “muddy and wet,” can those words reveal genetic similarities? A study of shirts worn by 45 men found a statistical association between shared descriptions and shared immune-related HLA characteristics for one perfumer, who provided the most detailed odor descriptions.
The same association did not appear across all five evaluators. This small 2007 study explored whether putting body-odor differences into words could help reveal biological clues.
Connecting immune-related types with words for odors
The study concerned the major histocompatibility complex, or MHC. This group of genes is involved in functions such as distinguishing the body’s own tissues from foreign material. In humans, the types investigated are known as HLA.
The paper asked whether the body odors of people with similar HLA types share qualities that can be described in words. Rather than relying only on liking ratings, the researchers used freely chosen descriptions of odor quality to explore correspondence with HLA.
The researchers typed HLA-A, HLA-B, and HLA-DR in 45 male students with a mean age of 24.6 years. For two days, the participants used unscented soap and detergent, avoided alcohol, smoking, and strongly scented foods, and wore untreated cotton T-shirts at night. The shirts were collected and stored frozen.
Two perfumers and three lay evaluators describe the odors freely
The shirts were thawed in containers, and two professional perfumers and three lay evaluators independently described their odors. The evaluators did not know the wearers’ HLA types, did not consult one another, and used their own vocabularies.
Another person who did not know the HLA types then grouped similar expressions, with help from each evaluator. For example, one evaluator’s terms were organized into groups such as dairy-like, fatty, dusty, wet fur, and sweet. Because the evaluators were not choosing from a common word list, their vocabularies and classifications differed.
The analysis considered all 990 possible pairs among the 45 men, relating whether they shared at least one odor descriptor to whether their HLA sharing exceeded the overall average. Because the same person appeared in multiple pairs, these were not treated as independent data from 990 people. Instead, a test randomly reassigned the correspondences to assess what might occur by chance. The researchers also corrected for multiple comparisons across the five evaluators.
The association appeared for the most detailed evaluator
Evaluator A, one of the perfumers, used more than three descriptors per shirt on average, providing the most detailed descriptions of the five evaluators. In this evaluator’s descriptions, pairs sharing words were associated with pairs sharing more HLA characteristics, and the result remained significant after correction for multiple comparisons.
The other perfumer and the three lay evaluators showed no significant overall association. The evaluators reported considerable difficulty in expressing differences in body odor in words.
The results suggest that detailed language may contain biological information, but they were not uniform enough to support the generalization that any perfumer could extract the same information. Differences in perception and in how people verbalize what they perceive may both play a role.
“Spicy” and “mud, wet” as leads for further investigation
On examining evaluator A’s descriptions more closely, the researchers found relatively high HLA similarity among wearers whose odors fell into the “spicy” and “mud, wet” groups. None of the 13 men described as spicy had HLA-A1, while HLA-A2 was more common than expected by chance. An association between the muddy, wet description and HLA-B14 was also suggested.
These findings came from closer exploration after the overall association had been identified. Many correspondences with HLA types were weak, and odors grouped under the same descriptor were not uniform. For example, the spicy group included shirts also described as milky, dusty, or fatty.
These two descriptors are therefore better understood as candidates for further experiments and chemical analysis than as a finished dictionary for identifying genotypes. The study had not measured particular odor molecules and established their connection to HLA.
Summary
In a study describing the body odors of 45 men, shared words were linked to shared HLA characteristics for one of five evaluators: the perfumer who gave the most detailed descriptions. Terms such as “spicy” and “muddy and wet” offered leads for closer investigation.
Describing body odor in words may help explore biological differences. At the same time, an important conclusion of this study is that the information obtained can vary with who describes the odor and how they express it.
The research was supported by the Roche Foundation and the Swiss National Science Foundation. The paper lists coauthors Sina Escher and Matthijs Van de Waal as affiliated with Firmenich at the time of the research.
Reference
Wedekind C, Escher S, Van de Waal M, Frei E. The Major Histocompatibility Complex and Perfumers’ Descriptions of Human Body Odors. Evolutionary Psychology. 2007;5(2). doi:10.1177/147470490700500206
