Always thirsty for new knowledge, I spent a few hours researching on google and Pubmed as a followup to this discussion, specifically in regards to my sense of smell. I’ll even throw a few links in here; yeah, I did that much research. Actually, I could cite all of my sources and turn it into a paper, but that sounds like way too much work for a forum post.
To start off with, the sense of smell is extremely complex. It is the least understood of the human senses, in part due to the lack of interest in its importance until a few decades ago and in part due to the complex mechanisms involved. This is disappointing because the scope and specificity of research is therefore somewhat limited. But it is also exciting, because there is so much more to learn. Nevertheless, I think I have learned what I need to know to continue improving my sense of smell to the best of my ability.
Olfaction (smelling) takes place at two structures known as the olfactory epithelium and olfactory bulb, located at the top of the nasal cavity. The health and sensitivity of these structures is central to the ability to smell. Anything that impairs these will consequently impair the ability to smell. The most obvious culprit is physical damage, such as head trauma. Any kind of bacterial or viral infection, either resulting in inflammation or degradation of the tissue may result in hyposmia (below normal olfactory ability). Interestingly, hyposmia is also a very early warning sight for Parkinson’s disease. It appears that any kind of neurodegenerative disorder will cause decreased regeneration of neurons in the olfactory bulb, resulting in it decreasing in size over time and therefore in decreased sensitivity to smells.
The olfactants (molecules that you can smell) must first get to the olfactory bulb, so proper airflow through the nasal cavity is very important. Congestion, resulting from infection or other cause, will have a negative impact relative to how severe the congestion is. Proper mucus production is important. Sniffing improves the threshold for detection. It is also important to note the we become numbed to things we smell all the time, so changing the environment could be good way to experience new stimulus and effect the growth of the olfactory ability. Therefore, frequently taking the time to really smell things and changing the environment occasionally should result in an increased ability.
A few other factors are worth noting. Exercise improves olfactory ability short-term, probably due to increase blood flow and opening up of the nasal cavity. So does fasting. The rise in ghrelin will cause an increased sensitivity; we smell food more and find it more appealing when we are hungry. I have personally both. Neither ability, sadly, is permanent.
An interesting paper I found (http://www.ncbi.nlm.nih.gov/pubmed/20603708
) looks at the effects of intermittent stimulus on perception of olfactory stimulus. Basically, it concludes that, while humans have a very good sense of smell, we actively sniff things so seldom and pay so little attention it that we do not notice things until they “jolt” us. For example, the detection level for ethyl mercaptan (put in propane to act as a warning signal) is as low as 0.009 ppb. The level actually put in gas, however, is 0.5 ppm, approximately 57,000 times the detection threshold. We need such a concentrated source to “jolt” our sense. It seems to me that simply paying more attention to what you can smell would result in, at the very least, an increased awareness.
There is good evidence that we can improve our sense of smell. To quote from the above study:
Humans are not only inherently good at odorant detection; they can further improve with practice. Repeated exposure to an odorant leads to decreased detection thresholds for a number of different odorants (Engen and Bosack 1969; Cain and Gent 1991; Dalton et al. 2002). Further- more, humans who were completely unable to detect the odor of androstenone developed the ability to detect it after repeated exposure (Wysocki et al. 1989).
One thing that I found very interesting was that hyperosmia, the ability to smell things really, really well, is generally considered to be a bad thing. The ability usually comes with a heightened sensitivity, that is that people who have this are often very sensitive to bad smells, so much so that it effects their life negatively. You can read more about it here http://www.medhelp.org/posts/Neurology/Hyperosmia/show/930893
. Come to think of it, not being able to smell very well is, in some ways, a blessing. Bad smells like smokers simply do not bother you. Eh, I’d rather have an awesome sense of smell and deal with the problems it brings.
The point here is to attempt to uncover ways to improve sense of smell. To review, if there is any infection or chronic nasal congestion, addressing that should help. Dietary choices might be able to benefit early stage health conditions like hypothyroidism and neurological problems, which can result in decreased sensitivity. Zinc deficiency can result in hyposmia, in which case eating oysters would help. Other than that, simply making a concerted effort to sniff things whenever possible and trying to breath more through the nose will definitely help. I will report on any future progress.
Sorry for the long post. Organizing it like this really helps me understand it. Hopefully you find it useful, and, at the very least, interesting.