Your Nose Knows More Than You Think

Compared with a bloodhound, our noses are inadequate. Humans have 5-6 million scent receptors in the nose. A bloodhound has 300 million. The portion of a dog's brain devoted to analyzing smells is about 40 times larger than ours.

Some birds also have remarkable beaks. Turkey Vultures can detect gases released by decaying carcasses. They have helped workers locate leaking natural gas pipelines, attracted by the sulfur compounds added to otherwise odorless gas.

But now, emerging research may change perceptions of human olfactory skills. Scientists have discovered, for example, that when people are frightened or under stress, their body odour changes. Some scientists believe that other people can detect that odour without realizing it.

An analysis of 26 studies involving more than 1,600 people found evidence that fear, stress and anxiety can be communicated through body odour. It might happen like this. You walk into a room. Someone is frightened. They haven't said anything or made eye contact. But somehow you become a little more alert yourself.

Body odours are being rebranded as “chemosignals”. And we can sense these signals in instances of fear and stress. Some research suggests we can also sense positive emotional states, such as happiness, from detectable chemical information.

How the molecular chemistry works isn’t yet clear. And critics point out that laboratory experiments are considerably more controlled than ordinary human life. But in thinking through your life, have there not been times when you “smelled” someone passing by in a peculiar way – not their odour, per se, but their emotions?

Scientists are also learning new things about our noses and disease. Our bodies constantly release hundreds of volatile organic compounds – chemicals that can be detected in breath, sweat, skin, urine and other bodily materials. When metabolism changes because of infection or disease, the chemical mixture can change too. It’s possible that diseases have distinctive chemical fingerprints.

This has produced extraordinary experiments involving dogs, electronic noses and laboratory instruments capable of identifying volatile compounds. Scientists are investigating whether these signatures could eventually help detect diseases earlier or more cheaply than conventional methods.

Parkinson's disease provides an intriguing example. Loss or reduction of the sense of smell – called hyposmia – is common in Parkinson's disease and can appear before the better-known movement problems.

Studies involving thousands of patients have found that smell testing can be effective in distinguishing Parkinson's disease from other conditions that can look similar. That doesn't mean a poor sense of smell diagnoses Parkinson's disease. Many healthy people have a poor sense of smell, especially as they get older. Nasal problems, medications, infections and other conditions can affect it. But it does mean that scientists are taking the nose seriously as a possible window into the brain.

Helen Keller, renowned American humanitarian who was deaf and blind from early childhood, referred to the nose as “the fallen angel”. She’d be pleased that modern science is beginning to restore the nose to a central focus.

So if you suddenly lose your sense of smell--or notice a substantial unexplained change--it may be nothing more than a cold, allergies, medication or aging. But you might want to mention it to your doctor.

And if someone passes by, and you can’t explain your interest, for better or for worse, go get a better sniff.