Loss of Smell and Taste with COVID-19
Dear Families and Friends,
There has been a lot in the news lately about a loss of the sense of smell during and after cases of COVID-19, especially in younger patients. I was recently featured on a television news segment about this problem, and I have seen kids with this in my practice. Since I got a lot of good feedback on my previous emails about COVID-19 testing and the serious inflammatory condition in children linked to the pandemic, I thought that I would update you all about how this happens, and what can be done.
Smell and taste have always been neglected in the world of medical science. There is a good deal of research done about the eyes and the ears; many resources and adaptive technologies are available for people with visual or hearing impairment. But problems with the senses of smell and taste (which are closely linked) can be very disturbing, causing serious quality-of-life issues. Not only can smell and taste problems interfere with our enjoyment of eating, they can be dangerous. These senses evolved to protect us; people with these issues are at risk since they can’t easily detect smoke, fumes or spoiled food. We are starting to understand that, just like many other viruses, the SARS-CoV-2 virus that causes COVID-19 can lead to olfactory dysfunction (OD). This is a loss of the ability to smell, or a change in how familiar substances smell. And this, as we will see, can cause problems with taste as well.
OD can be one of the earliest signs of COVID-19. Less commonly, it can be a lingering symptom that arrives later in the course of an illness, and it can last for some time after recovery. There is some evidence that patients with smell disturbances do better overall and are less likely to have a life threatening course of the illness. Results vary with different population groups, but it seems that more than half of people with COVID-19 experience an alteration in their ability to smell. Of course, no one has any long term experience with this disease, so much of what we do to treat OD and to give a prognosis is based on our experience with other infections. But still, early research suggests that this condition can be managed in a similar fashion. Keep in mind that if you or your child suddenly lose your sense of smell, that might be an early (or the only) sign of COVID-19. Contact your primary care doctor about the need for diagnostic testing, but in the interim self isolation would be appropriate. I think that it’s important to discuss some basic anatomy and terms here. There are a number of processes that are often lumped together in this area, but which are very different.
- Olfaction (smell): This is the sense that responds to odor molecules (odorants) in the air that flows through the nose. Typical odor molecules come from things like cinnamon, lavender or cloves. The molecules flow through the nasal airway (from the nostrils or the mouth) and interact with the olfactory nerve endings (the first cranial nerve), embedded in the lining of the roof of the nose. This generates signals that are carried out of the nose into structures on the underside of the brain - the olfactory bulb and tract. From there, the signals go into the brain, which then recognizes familiar scents.
- Gustation (taste): This is the sense that responds to chemicals that touch various parts of the mouth. There are five types of taste - sweet, salty, sour, bitter and umami (savory). The sense organs are taste buds, and they also send signals to the brain through cranial nerves. There are a number of nerve systems that carry these signals, but the main ones supplying the front of the tongue travel to the brain in the facial nerve (the seventh cranial nerve).
- Chemesthesis: This is often confused with taste and smell. Like them, it is a signal transmitted by nerves to the brain from chemicals in the mouth or nose. But it isn’t olfaction or gustation, it’s a type of touch sensation, picked up by structures similar to pain receptors. This involves different types of chemicals than those that trigger the taste and smell systems. For example, in the mouth they are triggered by capsaicin (from chili peppers) or menthol. In the nose, ammonia would cause this response. This is an important system to protect against toxins and other irritating environmental chemicals. These impulses are primarily carried by the trigeminal nerve (the fifth cranial nerve).
- Flavor: This is what you get when the brain combines the information from the olfaction, gustation and chemesthesis systems above, along with other touch sensations in the mouth (texture) to result in a recognizable sensation associated with specific foods. It is also why people will report problems tasting their food when they lose their sense of smell - there is nothing wrong with the taste buds, but the brain can’t put everything together without all of the information.
- Anosmia: The lack of smell, and a type of OD. Patients with anosmia don’t smell odorants at all, although they will respond to things like ammonia (which, as we discussed, is not really a smell response at high concentrations). Sometimes the word “hyposmia” is used to indicate a reduced but not completely absent sense of smell.
- Parosmia: A distorted sense of smell, and another type of OD. In many cases of parosmia, normal food can smell and taste bad enough to cause nausea.
- Phantosmia: Smelling things that aren’t there, also known as olfactory hallucination. This is more commonly associated with neurological conditions like seizures or Parkinson’s disease, head trauma, or less commonly, sinusitis.
So what actually causes OD? Loss of smell can be caused by blockage of airflow through the nose (“conductive” OD), or by damage to the olfactory bulb, or nerves themselves (“sensorineural” OD). Interestingly, the same terms are used to distinguish between the types of hearing loss. Conductive OD would be what you experience with a bad cold, allergies or sinusitis. The nose is so stuffed up that there isn't enough airflow for odor molecules to make it through the nose to be smelled. Sensorineural OD can be congenital, related to trauma or to a neurological process. In this context it would be the result of a viral infection. This is a well known symptom with many viruses, and it seems to be common in COVID-19, as mentioned above. Recent research suggests that in COVID-19, it is not the olfactory nerves themselves that are damaged by the virus, but the cells that surround and support them high up in the roof of the nose, in a small area known as the olfactory cleft. So while technically this is a type of localized obstruction, interfering with the function of the nerves, these patients don't have swelling and blockage of the rest of the nasal airway, and they don't complain of a stuffy nose. But because of injury to the supporting cells, the neurons may not be able to do their job transmitting odor information to the brain.
Conductive OD is treated in a similar manner to otters types of nasal obstruction - a diagnosis is made (allergies, sinusitis, etc..) and then specific medical or surgical treatment can be offered to improve the nasal airflow, which should also improve smell and taste. The sensorineural OD that follows COVID-19 would not necessarily respond to these measures. Fortunately, there is a lot of turnover of the tissue in the olfactory cleft - it is one of the areas in the body where nerve cells regenerate regularly and quickly. This is what make the prognosis for post viral OD fairly good.
With other viruses, recovery from OD may be quick (weeks), or it may linger for months or years. Of course, we don't know how long post-COVID OD will last, but most patients who recover do so in a relatively short time. There are still a few patients who - five months into the pandemic - still haven't recovered from this, but it will be years before we have good long-term data about this condition. During recovery, the sense of smell may vary from day to day. This can be frustrating, but there are some things that you can do to help improve the chances of recovering normal smell and taste.
One of the best online resources that I have found for people with OD is abscent.org, the website of a patient support organization based in the UK. While they provide information about many types of OD, they have a lot of material specific to COVID-19 associated smell and taste issues. Their instructions for olfactory training (OT) are particularly helpful.
OT is a way of rehabilitating patients with post-viral sensorineural OD. Familiar odorants are presented on a regular basis, twice a day, for several months. It is important to keep notes of your progress, which helps with the recovery process. You can make the kits to do OT yourself, or you can buy premade kits online. This is something that you can do on your own, without the need for a special therapist. It is important to find a quiet space and time without distractions, and to realize that improvement will not happen overnight. Don’t get discouraged when starting out. Mental visualization is important as well, so when practicing with each odorant, try to keep the source of that smell in mind, to help re-establish the nerve and brain pathways that let you recognize a certain scent accurately.
While there isn’t much evidence to support medical therapy in other forms of post-viral sensorineural OD, some success has been seen with vitamin A applied to the nose or omega-3 dietary supplements (which may help the nerve pathways regrow). Omega-3 also has some anti-inflammatory properties, which could limit injury to the cells of the olfactory cleft Of course, we still don’t know if these are effective with COVID-19 related OD, but it stands to reason that they might help if the mechanism of injury is similar, and there aren’t many risks to their use. It’s hard to give an overall prognosis, but information from pre-COVID research suggests that at least 2/3 of these patients get some recovery, even without treatment. Steroids are occasionally used for nasal conditions, but they are not recommended in this case, because of concerns about suppressing the immune system during infection with a potentially deadly virus.
So if your child has suffered a loss or change in smell or taste after an infection, I would be happy to see them to ensure that there is no nasal obstruction contributing to the problem. Following that, smell training and the supplements mentioned above provide an excellent chance of recovery. Just remember, if this happens to you, be especially sure that your smoke detectors are working and check the expiration dates on your food carefully!
I hope that you are all managing the stresses of this time. While the COVID-19 rates in the New York area have decreased considerably, we are watching outbreaks elsewhere in the country and trying to keep the medical and financial impact of the pandemic to a minimum. As our state governments move towards a phased recovery, be patient, and remember that it is important to monitor the data every day, and change policies accordingly. There is nothing wrong with making a call one day and walking it back the next. That isn’t hypocrisy or inconsistency, it’s governance based on ever changing information. Remember, this is a brand new virus that we are learning more and more about every day.
Even as we move back to a more “normal” existence, as we move towards socialization and outdoor meals, we need to do this safely. As the playgrounds and beaches reopen, we are all responsible for keeping the trends moving in the right direction. That means hand hygiene, mask use when indoors and/or near others, and applying the principals of social distancing when appropriate. There is no book that tells us exactly what to do in every conceivable situation, and we all are struggling to find the right balance between safety and the need for human contact. Each of us providing in-person services has come up with strategies to keep the risks to an acceptable level.
Yes, the safest thing to do is for everyone to stay in strict isolation until there is a vaccine, but it’s pretty clear that we aren’t going to do that for a number of reasons. All we can do is to make smart, informed decisions based on the best data and expert opinions that we have. Listen with an open mind. Give people the benefit of the doubt.
And always be there for each other, no matter how socially distant you are.
Best, Michael Rothschild, MD