Some have touted the symptom as a sign of COVID-19—but scientists have limited, inconclusive data in hand.
DOES YOUR EVERYTHING bagel suddenly smell like nothing? Is your shower gel missing its coconutty aroma? Growing reports suggest that the loss of your sense of smell, a condition known as anosmia, is a symptom of COVID-19. But scientists are not yet sure.
Citing a surge of anecdotal evidence from around the world, the American Academy of Otolaryngology-Head and Neck Surgery recently suggested that anosmia and related olfactory disorders be used to screen for cases of the new coronavirus. According to the academy, reports are mounting of people who tested positive for the disease but had no noticeable symptoms—other than a mysterious loss or reduction of their sense of smell.
Other experts in the medical community have pushed back, saying the coronavirus connection isn’t solid. So far, neither the U.S. Centers for Disease Control and Prevention nor the World Health Organization has added anosmia to its lists of COVID-19 symptoms. Even if there is a link, they say, simply losing your sense of smell isn’t enough to say for sure that you have the coronavirus.
“With COVID-19, smell loss might not be happening any more than with other upper respiratory infections,” says Steven Munger, director of the University of Florida Center for Smell and Taste in Gainesville.
Up to 40 percent of people with other viral infections, such as influenza or the common cold, experience a temporary loss of smell that usually reverses itself in a couple weeks. The condition is also common among people with allergies. Prolonged smell disorders, which affect 3 to 20 percent of the general population, are more prevalent among older people but can also be caused by severe head trauma, neurodegenerative diseases, or nasal polyps that block the flow of air and must be surgically removed.
“Why is smell getting so much attention?” Munger asks. “People are scared, and we’re trying to understand this disease. We’re trying to reach for things to help us recognize COVID-19 as early as possible.”
One pitfall of the early evidence on smell loss is that it relies on anecdotal reports, rather than long-term observations, which would be needed to establish a clear connection with COVID-19. Moreover, people in general have trouble characterizing their own problems with smelling or tasting because the two are so intertwined.
“They might say they have a taste loss when they have a smell loss, or they don’t understand how much loss they have,” Munger says. You can check if your taste buds are still working by taking a shot of a strong flavor, such as vinegar, salt, or sugar.
For example, a British study released last week collected COVID-19 symptom data from patients through an online app. The data show that almost 60 percent of the 579 users who reported testing positive for the coronavirus said they’d lost their sense of smell and taste. But a significant portion of patients who tested negative for the virus—18 percent of 1,123 people—also reported olfactory and taste troubles.
Another challenge is trying to understand what smell loss foretells of disease severity, given classic symptoms like fever and cough are clear indicators that the body is struggling. In an upcoming study in European Archives of Oto-Rhino-Laryngology, 85 percent of patients who experienced mild to moderate cases reported losing their ability to smell. That supports other early evidence that smell loss can occur in patients with few to no symptoms, says Eric Holbrook, director of rhinology at Massachusetts Eye and Ear. But he adds that the study is limited because it focuses only on those mild cases. It can’t say whether smell loss is also associated with more severe COVID-19 outcomes.
“Physicians are collecting data so quickly, but a lot of it is subjective data,” says Holbrook, who researches how to treat permanent smell loss. “I haven’t seen a careful study that looks at when patients get the diagnosis, and how severe it is, and how long the smell loss lasts.”
Can smell come back?
To better understand how smell loss manifests in COVID-19 patients, Holbrook and his colleagues have proposed a study that would administer tests for both coronavirus detection and smell ability for patients at Massachusetts General Hospital in Boston. Patients who report olfactory symptoms and whose sense of smell doesn’t return after their recovery from the coronavirus would be followed for several months afterward to collect valuable information on the persistence of the connection.
Luckily, losing your sense of smell from an infection doesn’t necessarily mean it’s gone for good. Viruses are believed to cause inflammation in sensory neurons in the nose, disrupting the nerve cells’ ability to transfer odor information to the brain. Unlike with our eyes and ears, though, damaged nerve cells in the olfactory bulb can regenerate throughout our lifetimes.
“That’s why if you lose your sense of smell, you often can get it back,” Holbrook says. “But we don’t know how long it takes to replace a neuron. It can take a year or two.”
COVID-19 is so new that researchers don’t know exactly when patients who report anosmia might recover their sense of smell.
To speed up recovery, some physicians offer a therapy called “olfactory training” that increases smell sensitivity and helps the brain correctly process signals. Patients inhale four odors, such as cloves, eucalyptus, lemon and rose, for 15 seconds at a time twice a day for three months and then switch to another set of scents for another three months. “You can use essential oils,” says Holbrook.
The sudden interest in how the coronavirus affects olfactory functioning is a boost for the field, which traditionally gets less research funding than the senses of sight and hearing.
The gift of olfaction is one of the joys of life, Holbrook says. Imagine not being able to bask in the aroma of roasting coffee or wafting jasmine. More importantly, the loss of the ability to smell becomes a public health issue when people can’t detect a gas leak, or smoke from a fire, or the putrid scent of spoiled food.
“Most people take the sense of smell for granted,” Munger adds. “When people can’t smell anymore, it can be a huge emotional loss.”