For most people who contract COVID-19, it is a short-term disease that lasts between one and four weeks. When symptoms last longer than 12 weeks, it is known as long COVID — also called post-COVID condition or long-haul COVID-19.

An acute (short-term) COVID-19 infection is known to cause sensory issues for some people, such as the loss of taste and loss of smell. These symptoms are also associated with long COVID. They can develop even without other common COVID-19 symptoms, such as shortness of breath and coughing.

COVID-19 and Loss of Smell

Researchers are still working to determine exactly how COVID-19 infection causes the loss of chemical senses like smell and taste. One theory is that the virus damages cells that provide support to the neurons (nerve cells) in the nose, known as sustentacular cells. Recent research from Harvard Medical School has found that these sustentacular cells can be infected with SARS-CoV-2, the coronavirus that causes COVID-19.

SARS-CoV-2 enters cells by binding to specialized receptors on the outside of cells known as ACE2. ACE2 receptors are found on the surface of epithelial cells that line the lungs and respiratory system, which is why COVID-19 impacts the lungs. However, these receptors are also found on the sustentacular cells in the nose. This has led researchers to suspect infection of these support cells causes the loss of smell, or anosmia.

The Immune System and COVID-19 Infection

A group of researchers from Italy found that inflammation may also play a role in the loss of smell due to COVID-19 infection. When cells become infected with the coronavirus, the immune system immediately recognizes the virus as foreign and generates a response. The innate immune system, the body’s first line of defense, reacts quickly.

The innate immune system is made up of many types of immune cells. One innate immune cell type is the macrophage, which is responsible for releasing cytokines that drive inflammation. Interleukin-6 (IL-6) is a cytokine released by macrophages that can create excess inflammation in COVID-19 infection.

Researchers have found a correlation between levels of IL-6 in the blood and the loss of smell and taste. One study of 67 people with COVID-19 reported that as levels of IL-6 decreased in the blood, a significant number of participants regained their sense of smell and taste.

Loss of Smell in Long COVID

Long COVID has been associated with chronic olfactory dysfunction (COD), meaning a person loses their sense of smell for longer than six months. A study from November 2021 estimated between 700,000 and 1.6 million people in the U.S. have experienced COD due to COVID-19 infection.

Another preprint study (not yet peer-reviewed) showed that 48 percent of men and 68 percent of women surveyed still had a decreased sense of smell roughly 200 days after the start of their COVID-19 symptoms. The researchers noted that many people also lost their sense of taste, although this symptom tended to resolve earlier. It was rare to lose the sense of taste without also losing the sense of smell.

Long COVID can also include another condition known as parosmia, where foods that normally smell good — such as fruit or coffee — now smell unpleasant. One study of 268 people found parosmia may occur in people who first lost their sense of smell due to COVID-19, and parosmia may start two to three months after the initial COVID-19 infection began.

COVID-19 and Loss of Taste

The sense of taste is interconnected with smell, and loss of both is a symptom of long COVID. In fact, loss of taste is reported in between 38.2 percent to 49 percent of acute COVID-19 cases, and it can continue to be an issue for many months after symptoms begin. Loss of taste is also called ageusia.

The process of tasting — known as gustation — involves many systems working together to create the sensation. Taste bud cells on the tongue have specialized taste receptors that pick up on different types of flavor, like sweet, sour, umami, bitter, and salty.

Taste bud cells also express ACE2, which allows them to be infected with COVID-19. As a result, infection and resulting inflammation can cause taste dysfunction. Similar to loss of smell, taste disorders from COVID-19 infection seem to be related to high levels of IL-6, which drives inflammation. This inflammation may damage the taste buds and bacteria that live on the tongue.

COVID-19 Effects on Vision and Hearing

While much less discussed than other COVID-19 symptoms, problems with vision and hearing can also occur after an infection. If these symptoms continue three or more months after the initial COVID-19 infection, they are considered to be part of long COVID.

Vision Symptoms

COVID-19 infection has been associated with several eye-related symptoms, including:

• Dry eye
• Blurry vision
• Itching and irritation
• Pink eye (conjunctivitis)
• Sensitivity to light
• Foreign body sensation
• Eye pain

One analysis of 38 studies found that at least one eye symptom occurred in around 11 percent of people who contracted COVID-19. However, the authors noted that some of these symptoms may not be directly related to the virus itself, but due to mask-wearing — air can travel upward in the mask, blowing over the eyes and irritating them.

Another study reported that people with long COVID can have nerve fiber loss in the cornea of the eye.

Hearing Symptoms

Issues with hearing have also been reported. One analysis of 12 studies found that 12 percent of people with acute COVID-19 experienced vertigo, 4.5 percent heard ringing in the ears (tinnitus), and 3 percent had hearing loss. However, the researchers also cautioned that more research is needed. These symptoms may be caused by inflammation or by an infection in the inner ear cells which control hearing and balance.

Treatments for Loss of Senses

Losing a sense can have a negative impact on your quality of life, especially during the pandemic. There are treatments available to help you manage your symptoms and even “retrain” your senses.

One treatment being used to bring back the sense of smell and taste is olfactory retraining or “smell training.” In an article for University of Colorado Health, Dr. Jennifer Reavis Decker notes that the best chance of improving your sense of smell is within six weeks after losing it. Smell training uses strong scents — like clove, eucalyptus, lemon, and rose — which are inhaled for 20 seconds at least twice a day for three or more months.

If you are experiencing changes to your senses of smell, taste, vision, or hearing after a COVID-19 infection, talk to your health care provider. Your health care team can help you come up with a treatment plan.

Talk With Others Who Understand

On myCOVIDteam, the social support network for those recovering from the effects of COVID-19, you can connect with others. Members come together to ask questions, give advice, and share their stories with others who understand.

Have you lost your sense of taste or smell due to COVID-19? Share your experience in the comments below, or start a conversation by posting on myCOVIDteam.