Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior

Occlude one nostril by pressing on it from the side and sniff in, and then occlude the other and sniff in. Do you sense a difference in flow? ... If you were to do that repeatedly, you would find that your high-flow nostril and low-flow nostril alternate every 2 and a half hours on average.

We exposed participants to these tears ... When you sniff them, you have a pronounced reduction in testosterone within about 20 minutes, half an hour ... You have about a 14% drop in free testosterone.

I get a lot of emails from people who have lost their sense of smell, because it's very distressing ... Basically, the rule of thumb is that if you don't get it back within a year to a year and a half, you'll never get it back.

Basically, there's something about the first time you experience a smell that generates a particularly robust representation more than other sensory stimuli ... There's something about the first exposure to a smell in terms of the brain encoding that etches it into our being.

Humans emit a particular body odor when they're in a state of fear, and this body odor influences other humans—in effect, increasing their autonomic arousal, their sympathetic state. So, in effect, you could say that fear is contagious.

Airborne molecules travel up our nose a distance in the human of about 6 or 7 cm... where they interact with... a sheet of receptors .... We have about 7 million such receptors lining a structure known as the olfactory epithelium.

Loss of the sense of smell is one of the, if not the, earliest sign of neurodegenerative disease. So, for example, in Parkinson's disease, there's loss in the sense of smell probably 10 years before any other symptom.

When you expose a pregnant mouse at an early critical stage of the pregnancy—I think up to about day 3—if you expose the pregnant mouse to the odor of what is referred to in technical terms as the non-stud male, that is a male who did not father the pregnancy, she will miscarry the pregnancy; she will abort it.

There's a number of papers published about this on PubMed that alpha-lipoic acid can accelerate the recovery of smell, and so that's something that worked successfully for me.

Humans have an utterly remarkable sense of smell ... Mercaptans, which are added to cooking acids ... Our detection threshold—that is the level at which we can detect it—is 0.2 parts per billion.

We think that nasal inhalation is timing and driving a lot of aspects and patterns of neural activity and cognitive processing.

There's at least one theory, particularly about Alzheimer's disease, suggesting that Alzheimer's may be the result of a pathogen that enters the brain through the olfactory system.

We also smell through our mouths, actually. There's a process referred to as retronasal olfaction where odorants come up through the back of our throat and out of our nose the reverse way.