Why Does COVID-19 Have A Lasting Impact on Loss of Smell?

Imagine waking up one day and not being able to see the world, hear its sounds or feel what you touch. This would be life-altering, right? You may not put smell or taste in that same category, but together, they make up 40 percent of your sensory input. 

Many of the long-term issues for COVID-19 survivors aren’t related to the lungs or brain. Instead, many people are stuck with smell disorders such as anosmia — a loss of smell — and hyposmia — a decreased sense of smell — that also affect how they experience food. To better understand this growing concern, we explored the science behind the loss of smell, how long it takes for these senses to return and what you can do to start regaining your smell.

How do smell and taste work together?

When COVID-19 cases mounted in 2020 and symptoms became more apparent, many people thought they were experiencing a loss of taste. Why? Everything tasted bland and they couldn’t smell the aromas of foods they loved to eat.

What they were experiencing was a loss of smell — what you smell makes up a large part of the food experience. What you taste comes from the thousands of taste buds in your mouth and oral cavity as food particles dissolve in saliva. These tastes fall under four categories: bitter, salty, sour and sweet. As for your smell, molecules called odorants travel through your nose to the olfactory nerve, which helps signal to the brain what you’re smelling.

Although taste and smell are separate, the brain connects the two so you can experience flavor. However, most of your food’s flavor comes from smell, which is why you may be uninterested in eating when losing your sense of smell. Texture and the warming or cooling association from certain foods, such as hot sauce, also make up the entire flavor experience.

For example, the texture and smell of a pineapple can help you differentiate it from a strawberry. But when you lose that ability, you would only be able to taste the sweetness associated with each and you would miss out on the entire flavor experience.

This is where the misconception comes into play. Losing or having your sense of smell reduced doesn’t mean you can’t taste. Your perception of it is simply altered. 

The actual loss of taste is called ageusia, which is rare. Patients experiencing this can’t tell the difference between the saltiness of a potato chip or the sweetness of a cookie. Your taste receptors don’t have protein receptors needed for the virus to attack, but other supporting cells in your mouth do, which may explain why some COVID-19 patients briefly deal with ageusia. 

Why does COVID affect taste and smell?

When you develop a cold or viral infection, the subsequent immune system response can often cause inflammation in your nose and lead to an acute loss of smell that lasts a few days or a week.

Determining the cause of why COVID-19 causes a loss of smell isn’t as easy to understand. Initially, medical professionals thought it was due to damage to the olfactory neurons. The theory was SARS-CoV-2, the virus that causes COVID-19, would travel through the nose and up toward the brain, damaging these essential nerves in the process. Since nerves need time — measured in months — to regenerate, this seemed like a plausible explanation.

Instead, more research on the subject indicated damage to the cells that support and assist the olfactory neurons, called sustentacular cells, was to blame. According to Harvard Health, researchers discovered a protein receptor called angiotensin-converting enzyme (ACE2), which SARS-CoV-2 uses to enter cells, was present in sustentacular cells but not in olfactory sensory neurons. In other words, the virus attacks the cells around the olfactory neurons but not the neurons themselves.

Once infected, the support cells can’t provide nutrients and support to the olfactory neurons, which in turn damage them to the point where they can’t send messages from the nose to the brain.

The findings indicated the majority of anosmia cases won’t be permanent since the olfactory nerves themselves aren’t directly damaged.

Theories on long-term damage

While this is good news, it still doesn’t explain why some patients have long-standing issues with their sense of smell, some of which become permanent. 

One hypothesis relates to a recent observational study conducted by the University of Oxford and Imperial College in the United Kingdom and the National Institutes of Health in Maryland. The study, albeit from a small pool of 394 people, found COVID-19 led to a “loss of grey matter in limbic cortical areas directly linked to the primary olfactory and gustatory system.”

The findings suggest COVID-19 may shrink parts of the brain, including the areas that communicate with the olfactory system. It’s unclear if this is a result of the virus itself or the symptoms COVID-19 causes.

One of the more interesting discoveries has been who anosmia affects. The Journal of Internal Medicine analyzed more than 2,500 patients in January 2021 and found 86 percent of COVID-19 patients with mild symptoms developed anosmia, but just 4 percent to 7 percent of patients with moderate to severe symptoms experienced a loss of smell.

Then there’s also the component of how preexisting conditions may serve as risk factors. For example, a history of using tobacco products, having dental or nasal problems or experiencing a head injury can all factor in. Pre-existing conditions such as Alzheimer’s disease or Parkinson’s disease may also play a role in losing your smell.

Why do I have a weird smell in my nose after COVID?

This is a question many COVID-19 patients have after losing their sense of smell for an extended period. Whether it’s smelling rancid garbage when garbage isn’t around or a strong coffee odor when none is present, many people report experiencing weird smells in their nose.

Depending on the specific symptoms, you may be experiencing dysosmia, parosmia or phantosmia — three types of smell disorders. Dysosmia is a distorted sense of smell, while parosmia is a misperception of existing odors or something normally pleasant smells bad. Phantosmia, on the other hand, is when you smell odors that don’t exist.

Here are a few examples. If your brain thinks it’s smelling rotten meat when no rotten meat is around, you’re experiencing phantosmia. If you smell a cake and your brain perceives it as something off-putting, you’re experiencing parosmia because the smell isn’t what you expect.

While many COVID-19 patients are reporting distorted smells, others are smelling things that don’t exist. Think of this as muscular pain that isn’t actual pain — it’s all in your head, quite literally. By definition, it’s an olfactory hallucination. In some patients, these smells are persistent, while others smell these odors from time to time.

Although these smell disorders can be frustrating, especially if they interfere with some of your favorite foods, it generally indicates you’re headed in the right direction. As olfactory neurons begin to reconnect with the brain, they may misfire signals at first, which can cause sensory errors before correcting themselves. 

Can COVID-19 cause permanent loss of smell?

Unfortunately, some people won’t regain their sense of smell following a bout with COVID-19. But this problem isn’t limited to COVID-19. Upper respiratory infections from the cold, flu or other viruses can also cause permanent damage.

The good news is 90 percent of people who initially lose their sense of smell see improvements within four weeks, according to the Mayo Clinic. The Journal of Internal Medicine also studied more than 2,500 patients and found 95 percent regained their smell within six months.

Of the remaining 5 percent to 10 percent, this is where patients either don’t regain their smell or it comes back in a reduced or distorted manner.

How to regain sense of smell and taste after COVID

Acute cases of anosmia may benefit from nasal sprays or steroid sprays to reduce inflammation. However, there isn’t a proven treatment for people with a prolonged loss of smell.

Olfactory training may be your best bet to work your way back to pre-COVID smells. Much like any other type of therapy that uses repetition to retrain your body, olfactory training can help your body create new nerve pathways.

It may seem silly to sniff something over and over to help retain your brain, but the idea of smell training isn’t something new — it was first introduced as an idea in 2009.

The central focus of olfactory training is to use primary odors to retrain the nose. The scents, coupled with your memory of how things smell, helps jump-start the process. There are a few basic smells — flowery, fruit, aromatic and resinous — and another half dozen or so more that include more foul smells like pungent and decayed.

To perform the olfactory training, begin smelling items in these categories, usually in the form of an essential oil, for 20 seconds while taking a deep breath. As you deeply inhale the scent, visualize what the item looks like and what it smells like. Then repeat this process with the remaining scents.

Perform this training several times a day, and you may begin to see improvements in three to six months.

If you or a loved one has experienced a loss of smell, contact your primary care physician or schedule an appointment with an ear, nose and throat doctor (otolaryngologist) at INTEGRIS Health.