The acute loss of smell and taste are hallmark symptom that can follow COVID 19 infection. It is estimated that at least 80-90% of COVID-19 patients had experienced anosmia (absent sense of smell), hyposmia (reduced sense of smell) parosmia (distorted sense of smell) or ageusia (loss of taste). Smell complications can be one of the most persistent symptoms of long COVID-19. It is estimated that most people will recover their sense of taste and smell in a matter of weeks after onset of COVID-19, about 20-30% will continue to suffer the loss of smell and will not recover completely.
Smell, Taste and Long COVID Biology
Smell and taste are mediated by two sense organs. Smell is mediated by odor receptors in our nasal epithelium. The olfactory nerves are a part of the nasal epithelium and are activated by specific chemicals. When the nerves are activated, they send signals to the brain that identify the odors we perceive. Hundreds of different receptors can respond to unique chemicals, and when multiple odorants are present, multiple receptors activate. It is estimated that humans may be able to distinguish up to one trillion distinct odors.
Taste, on the other hand, is regulated by the receptors known as taste buds, which are located on the tongue and back of the throat. These cells are thought to respond to salty, sweet, sour/acidic, bitter and umami/” meaty” stimuli. When stimulated, these cells send signals to the brain, causing us to become aware of our taste perception. Taste and smell are inextricably linked because detecting food flavor necessitates the activation and convergence of both taste and smell receptors. Anyone who had experienced a “stuffy nose” or loss of smell can attest of “tasteless” food or that food tastes different. These individuals may still be able to identify tastes of saltiness or sweetness, but not the complex tastes of many foods.
Loss of smell and taste can be categorized as a neurological complication of the SARS CoV-2 infection. Local inflammation, nasal obstruction, damage to the organs (olfactory centers in the brain and/or olfactory receptor neurons) have been suggested as mechanisms related to COVID-19 related anosmia.
Managing loss of smell and taste
It is important to keep tasting food, as taste preferences can change over the course of the long COVID syndrome. Adding a variety of herbs or spices, as well as being persistent in adding flavor to food, can help in the recovery of senses of smell and taste.
Mouth rinsing and gargling with water or chewing sugar-free gums can help people whose loss of taste is due to mouth dryness. Those who find their food tastes “too sweet” can add citrus flavors to counteract sweet taste sensation.
Nasal irrigation can help by flushing our allergens and mucus from the nasal cavity.
Many people will not require any treatment; however, medical referral should be considered in those whose impaired taste and smell sensations last beyond 2 weeks.
Therapeutic Treatment
Olfactory Training for Loss of Smell
Individuals who have loss of smell due to COVID syndrome can benefit from olfactory training or smell retraining therapy. This consists of actively sniffing four strong scents every day, spending about 20 seconds on each scent. The following four scents often work well:
- rose
- eucalyptus
- lemon
- clove
Patients should sniff each smell, without a break, for at least 20 – 30 seconds, twice a day for at least 24 weeks. Smell retraining may be most effective when the same four scents are used without alternating. To get the best results, an individual should concentrate and give full attention to the smell for the entire 20 seconds. In case those scents are not discernable, try remembering what they smell like.
Another good options to consider for smell retraining is ground coffee, vanilla, mint or ginger.
Ginger has a distinctive, pungent scent that may make it beneficial in smell retraining. Dirking ginger tea may also help reduce inflammation and reduce excess mucus that may block the nasal airways.
The olfactory training has demonstrated to be effective in the recovery of smell sensation in patients with long COVID syndrome. It is thought to work by repeatedly stimulating olfactory neurons, which, unlike the overwhelming majority of other nerve cells in the brain, have the ability to regenerate.
Immuno-Physiological Therapy
The Anti-inflammatory diet, combined with carefully chosen targeted supplements and vitamins like Vitamin A, C, D, Zinc, Melatonin, Quercetin, Omega-3, N-Acetyl Cysteine (NAC), Glutathione, Astragalus, Resveratrol can have a profound effect on lowering overall inflammation in the body.
Pharmacologic Therapy
Neuroprotective and anti-inflammatory agents such as intranasal or oral corticosteroids, statins, minocycline, intranasal vitamin A, omega-3 and melatonin may help with regeneration of olfactory receptor neurons.
Additional ongoing trials include treating persistent smell and taste symptoms with sodium citrate, Oxytocin nasal spray, and the use of hyperbaric oxygen, intranasal PRP plasma injections and vagus nerve stimulation
