Making snotty scents

Snot is often what shows up after a hard sneeze. It’s a constant companion of allergies and the common cold. It’s wet, sticky and — to most people — best left up the nose.

But snot, or mucus, also contains many different kinds of proteins. Those proteins may play an important role in something else that happens in the nose: smelling. In a recent study, researchers from Japan’s University of Tokyo showed that proteins in mucus change the makeup of odors before those scents even make it to smell receptors. Smell receptors are also proteins. They stick out from the cells that send signals about a smell to the brain, which identifies the odor.

That means that sticky, wet, gross mucus might have a more glamorous role: It may be important for smelling smells.

It seems natural to assume a connection between smells and snot. After all, the human nose is home to the sense of smell — and is an exit for snot. But “most people and most scientists pay no attention at all to mucus,” neuroscientist Leslie Vosshall told Science News. Vosshall is at Rockefeller University in New York City and was not involved in the recent study.

Scientists suspect that some molecules in mucus carry smells to other parts of the nose, where they can be detected. Other molecules in snot are enzymes, which start chemical reactions. Some enzymes may protect the body by chopping toxic substances — such as inhaled chemicals — into smaller, safer chunks. But until now, scientists did not know whether this chopping action could affect the smell of something.

To learn about smells and mucus, the researchers experimented on mice. They removed mucus from the noses of mice. Then, they mixed in chemicals that have particular odors. One of these chemicals was benzaldehyde, also known as artificial almond oil. After five minutes in mouse snot, the benzaldehyde had broken down into two chemicals — one that had no smell and another that did.

When the researchers inactivated the enzymes, by boiling the mucus, and then tried the same experiment again, the benzaldehyde did not break down.

That part of the experiment showed that the mucus could change the chemical composition of odors. Next, the researchers showed that the mice brains also register this difference. For this part of the project, the scientists “turned off” the mucus chemicals in the mice noses that usually chop up odorous molecules. As a result of this change, the mouse brains reacted differently than they did before — showing that their brains had picked up on the change.

The researchers also used mouse behavior to show that mucus changes the smell of something. For this part of the experiment, they used mice that had been trained to identify certain smells. (In training, the mice had been given treats when they went to those smells. After training, the mice naturally went back to those smells, hoping for more treats.) When the scientists turned off the important molecules in the mouse mucus, the mice were unable to recognize those favorite smells.

Scientists don’t know whether the molecules in mucus work the same way in people. Human mucus does have many of the same proteins as the mucus in mouse noses, so it’s worth investigating. Early studies do suggest that human snot can change odors, so stay tuned. And cover your nose when you sneeze.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

olfactory Of, relating to, or contributing to the sense of smell.

proteins Fundamental components of all living cells, including many substances, such as enzymes, hormones and antibodies, that are necessary for the proper functioning of an organism.

molecule A group of like or of different atoms held together by chemical forces.

enzyme Any of numerous proteins produced by living organisms that function as biochemical catalysts.

bacteria Single-celled microorganisms that vary in terms of morphology, oxygen and nutritional requirements, and motility. They may be free-living, saprophytic, or pathogenic in plants or animals.