From fragrant to popcorn: US scientists identify 10 categories for smells

Forget the unique aroma of fresh coffee, wild lavender or cut grass, according to US scientists there are just 10 basic smells.

In claims that would confound French perfumers and will prove controversial, a new study has reduced the thousands of odours humans can detect to a handful of categories.

According to Professors Jason Castro, of Bates College, and Chakra Chennubhotla, from the University of Pittsburgh, some 144 smells they tested could be grouped into 10 categories - including “fragrant, popcorn” and “chemical”.

The scientists told the PLoS One journal that the new categories allowed people to build smells and could lead to the ability to predict a smell based on its chemical structure.

Working with a 1985 list of odour “character profiles”, researchers applied mathematical methods to simplify the olfactory information.

They described it as similar to compressing digital audio or image files. “You have these 10 basic categories because they reflect important attributes about the world - danger, food and so on,” Prof Castro said. “If you know these basic categories, then you can start to think about building smells.”

He added: “It's an open question how many fundamental types of odour qualities there are. This is in striking contrast to olfaction's 'sister sense', taste, where we know that five basic qualities seem to organise sensations.”

He added that the theory would need to be tested on more complex aromas - such as perfumes - and that natural scents were likely to be a “complex blend” of the 10 categories.

The science of smelling has long confounded experts with many claiming it still remains a mystery. It was only in 2004 that it was discovered how the brain recognises and remembers thousands of different odours thanks to a large gene family that controls specialised protein receptors in the nose.

Prof Richard Axel, of Columbia University, and Prof Linda Buck, of Fred Hutchinson Cancer Research Center in Seattle, were awarded the Nobel Prize for their discovery.

The categories

1 Fragrant

2 Woody/resinous

3 Fruity (non-citrus)

4 Chemical

5 Minty/peppermint

6 Sweet

7 Popcorn

8 Lemon

9 Pungent

10 Decayed