Human noses can distinguish up to one trillion different scents, according to new research. 

Andreas Keller, from Rockefeller University's Laboratory of Neurogenetics and Behavior, led the study. He and his team tested the ability of volunteers to distinguish between a wide range of different smells. Using 128 scented chemicals, such as orange, spearmint, and anise. Keller and his team carefully studied the ability of people to recognize combinations of odors.

Before this experiment, most researchers usually estimated human noses were capable of distinguishing 10,000 types of smells. This number was based on research done in the 1920's, which was based on some outdated assumptions. A more accurate study of the number of smells discernible to humans has never before been undertaken. Most modern investigators believed that estimate from almost 100 years ago would need to be revised upward. 

After Keller and his team completed their experiment, calculating at least one trillion smells could be detected by human senses. The researchers even think that estimate may be too low. 

"The message here is that we have more sensitivity in our sense of smell than for which we give ourselves credit. We just don't pay attention to it and don't use it in everyday life," Keller said

Smell is difficult to study, because it is so complex. Vision and hearing can be limited to one tone or symbol to check for acuity. But, most smells people encounter in everyday life are composed of dozens or hundreds of component scents. A rose, for instance, has 275 smells that make up its distinctive aroma, although a few predominate. 

Keller and his team combines two or more odors in samples, asking volunteers to identify single ingredients within the samples. Each volunteer was provided with series of three vials. Two were identical mixtures, while the third contained a different adulterant to a scent. Researchers asked volunteers to choose the vial that was different from the other two. 

The study "...demonstrates that the human olfactory system, with its hundreds of different olfactory receptors, far outperforms the other senses in the number of physically different stimuli it can discriminate," researchers wrote in the study.

Traditional ideas that human noses may be poor compared to other animals may need to be revised in the light of this new finding.

The study group consisted of 26 men and women, ages 20 to 48. The volunteers came from a wide range of ethnic backgrounds and racial groups. 

While we may be able to detect up to one trillion different scents, the human eye can only see 7.5 million colors, and we hear just 340,000 different musical tones.

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