Scientists have long known that people perceive scents differently. But emerging evidence from several large-scale studies shows that the variation is larger than previously known. It turns out that people differ in how they perceive many if not all odors, and most of us have at least one scent we cannot detect at all. “Everybody’s olfactory world is a unique, private world,” says Andreas Keller, a geneticist at the Rockefeller University.

Over the course of evolution, partly because humans grew more reliant on vision and smell became relatively less important, the genes encoding our 400 or so olfactory receptors began to accumulate mutations. Once a gene has accumulated enough mutations, it becomes a “pseudogene,” notes geneticist Doron Lancet of Israel’s Weizmann Institute of Science, meaning it no longer encodes a functioning receptor. Different people have different combinations of pseudogenes, however. “You end up with a bar code situation, whereby each individual has a slightly different bar code,” he says.

That genetic variability seems to translate into behavioral variability. When  Keller and his colleagues asked 500 people to rate a panel of 66 odors for intensity and pleasantness, they gave the full range of responses—from weak to intense and from pleasant to unpleasant. In an ongoing study at the University of Dresden, Thomas Hummel and his associates have tested 1,500 young adults on a panel of 20 odors and found specific insensitivities to all but one—citralva, which has a citrus smell. Based on these findings, Keller suspects that each person has an olfactory blind spot.

These studies have wider implications than smell, Lancet says. Because several genes contribute to the detection of most odors, understanding the genetics of olfaction and the way mutations spread in a population is yielding insights into the mechanisms of poly­genic diseases such as coronary heart disease and diabetes.

This article was originally published with the title You Smell Flowers, I Smell Stale Urine.

5 Comments

1. 1. grandpa 09:55 AM 1/20/11

   As a bit of an aside, for a time I grew roses of several different varieties. Each variety had a distinct fragrance from the others, but all were easily identifiable as a rose fragrance. I always thought that strange.

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2. 2. jtdwyer 12:23 PM 1/20/11

   So, even though a person might stink really bad, there's a perfect mate out there somewhere who can't tell?
   There should be an app for that!

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3. 3. Tom Gable 04:00 PM 1/20/11

   This explains the wide variation in tasting note descriptions by wine writers. For example, the same Cabernet Sauvignon from the Central Coast of California was described as "rubber boot" by one judge in a wine tasting and "herbaceous and bell pepper" by another. Some are turned off by "over-ripe prunes" from high-alcohol (14.8 and higher) Cabernet and Bordeaux-style wines while others revel in the "fruit forward intensity with blackberries, cassis and mint." As wine experts have always noted: the nose knows.

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4. 4. bucketofsquid in reply to Tom Gable 01:22 PM 2/1/11

   Interesting observation. Unfortunately I'm out past the "rubber boot" end of the scale. Even a hint of alcohol in a drink tastes strongly of decay to me and thus ruins any flavor it may have.
   
   I have pretty strong reactions to most prefumes and colognes as well. I will take the stairs to avoid being in an elevator with someone that wears the stuff. If a person bathes and wears clean clothes they tend to smell good to me. Perfumes and the like just smell terrible and I have to wonder what they are hiding.

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5. 5. ptarmigan 10:18 PM 11/7/11

   I cannot smell sewage. I'm told my sense of smell is otherwise fine. I can smell everything else. It is a fortunate sensory "blind spot," as I do child care and deal in dirty diapers all day long. =)

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