Ian Spohn, ND, is a staff naturopathic doctor for Energique who enjoys challenging the dogmas of both conventional and alternative medicine. He is a passionate supporter of the paleo diet and classical homeopathy.
Anosmia, or loss of smell, is a common symptom of numerous upper respiratory infections, and in some cases can persist long after the infection resolves. It is believed that certain viruses, such as herpes simplex virus 1, can actually infect the bulbs of olfactory sensory neurons themselves, and even use the olfactory nerve as a route to infect the brain. However, most respiratory viruses lack the capability to do this, and when anosmia persists following an upper respiratory tract infection, this is typically the result of local inflammation causing damage to the olfactory epithelium – in other words, the dense array of odor receptor neurons which line the nasal cavity. Any infection which results in a high pathogen load within the nasal cavity, which would include most viral respiratory infections, can damage olfactory neurons and lead to loss of smell. In some cases, this can be a temporary result of local congestion and mucus creating a physical barrier between odor molecules and the specialized nerves that detect them, but when smell does not return to normal soon after the infection, this implies a destruction of the nerve endings themselves. It is believed this damage is simply the result of local inflammation required to fight off the virus, and the good news is that damaged olfactory neurons are able to regenerate. In fact, they regenerate relatively well compared to other nerves, and as a natural process this can be supported and perhaps even accelerated by holistic treatments.
The reason olfactory nerves can be healed with relative ease is that they are actually designed to continually die and regenerate throughout life. It is a peculiarity of the olfactory sense that every olfactory neuron is specialized to detect only one specific type of odor molecule. Compared to the tongue, whose sensory nerves can detect perhaps five different tastes, it has been estimated that the human nose can detect at a minimum ten thousand, and according to some estimates up to one trillion different types of odors. This means that at any given time, there are at least ten thousand different types of sensory neurons in the nose, each adapted to detect a specific odor. It is also a fact that our sensitivity to and ability to detect a given odor is a direct result of how many sensory neurons we have adapted to it. When one type is repeatedly stimulated by a certain scent, its life is prolonged, whereas receptors that do not become stimulated by their odors tend to die off. This allows the nose to essentially “prune” itself to specialize in whatever odors become most relevant in the environment, while simultaneously retaining the capacity to learn to detect new odors. It also allows new synaptic connections to be forged with other areas of the brain, allowing us to associate new memories with old odors, or alter their emotional salience. This explains why the smell of popcorn perhaps might fill you with joy, as it calls to mind fond memories of taking your sweetheart to the movies, but then evoke nothing but grievous heartache after the breakup, or turn forever to callous loathing ever since that horrible summer you had to work there every day, smelling it constantly as you stood behind that concession stand at a job you hated.
Because sensory neurons regenerate, the loss of smell following an upper respiratory infection can be expected to eventually return, though sometimes it can take months before this happens. In these cases, natural treatments may be of benefit. One promising approach is vitamin A supplementation, for which there is presently a research trial ongoing in the U.K[i]. Vitamin A is crucial for proper cell differentiation, being required for constantly regenerating epithelial cells to specialize and form their target tissues. Highly specialized epithelial cells in the retina do not become photoreceptors in the absence of vitamin A, leading to blindness, and specialized respiratory epithelium becomes less ciliated in vitamin A deficiency, increasing the risk of respiratory infections. Because post-viral anosmia results from damage to the specialized, ciliated sensory epithelium lining the nasal cavity, it stands to reason that vitamin A deficiency might impair this tissue’s ability to regenerate and restore the sense of smell, especially since bouts of infection tend to lower vitamin A reserves. Could a delay in regaining one’s sense of smell be due to a vitamin A deficiency, and could supplementation restore it faster? While unknown at this time, research is currently seeking to answer this question.
Besides vitamin A, botanicals offer another potential approach to support the regrowth of olfactory nerves. Like other nerves, the sensory nerves in the nose rely on axonal elongation to regenerate, a natural process controlled by certain growth factors. Among the most important and well-studied of these is brain-derived neurotropic factor, BDNF. There is research showing that a number of herbs can increase levels of BDNF and accelerate axonal regeneration, making them useful candidates to support the natural repair processes involved in restoring olfactory nerves. Some of these herbs include Ginkgo biloba, Hypericum perforatum, Olea europaea, Panax ginseng, and Withania somniferum[ii]. Most of these herbs have been used traditionally to support different aspects of the nervous system, and it is likely that any herb that is tonic, protective, or trophorestorative to the nervous system would be useful to promote olfactory nerve regeneration.
Homeopathy has also been used as a traditional treatment for loss of smell. There are numerous homeopathic remedies that may be of benefit, with Nux vomica, Pulsatilla, and Zincum Metallicum being among those most frequently employed[iii]. There are actually case reports of anosmia being caused by the use of intranasal zinc for immune support[iv], so if the crude substance can impair one’s sense of smell, it stands to reason that remedies like Zincum Metallicum might be able to restore it along homeopathic principles. Another possible approach would be to use sarcode remedies and organotherapy to support the nervous system, or even the nasal mucosa specifically. Mucosa Nasalis Suis, a sarcode remedy made from nasal mucosa itself, has been officially monographed in the Homeopathic Pharmacopoeia of the United States and has been employed to support the nasal mucosa according to some of the theories of organotherapy arising from the French school of homeopathy.
Beyond this, smell retraining therapy is a relatively novel approach to treating anosmia and is currently being recommended by some doctors to help restore the loss of smell in cases resulting from some recent viral infections[v]. As has been mentioned, the life of olfactory nerves is prolonged when they are regularly exposed to their target odor molecules, and it seems that this can also help them regrow. It is specifically recommended to use a variety of scents from different odor categories, such as rose (floral), lemon (fruity), clove (spicy), and eucalyptus (resinous)[vi]. Using a variety of essential oils or other strong-smelling substances, patients can be instructed to sniff the fragrance for several seconds while focusing intently on their memory of what it should smell like, and repeat this up to several times per day, as a form of physical therapy for the nose. It is recommended to continue for several months, to allow for the time required for sensory neurons to grow.
[i] Roberts, Michelle. Vitamin A Treatment Trial for Covid Loss of Smell. BBC News Online 9/29/21, accessed 10/29/21 at https://www.bbc.com/news/health-58705938
[ii] Sangiovanni E, Brivio P, Dell'Agli M, Calabrese F. Botanicals as Modulators of Neuroplasticity: Focus on BDNF. Neural Plast. 2017;2017:5965371. doi:10.1155/2017/5965371
[iii] Murphy, Robin. Homeopathic Clinical Repertory, 3rd Edition. Lotus Health Institute: Blacksburg, VA, USA, 2003. Pg. 1793.
[iv] Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope. 2006 Feb;116(2):217-20. doi: 10.1097/01.mlg.0000191549.17796.13. PMID: 16467707.
[v] Whitcroft KL, Hummel T. Olfactory Dysfunction in COVID-19: Diagnosis and Management. JAMA. 2020;323(24):2512–2514. doi:10.1001/jama.2020.8391
[vi] American Academy of Otolaryngology-Head and Neck Surgery. Smell Retraining Therapy. Accessed online 10/29/21 at https://www.enthealth.org/be_ent_smart/smell-retraining-therapy/
Any homeopathic claims are based on traditional homeopathic practice, not accepted medical evidence. Not FDA evaluated.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.