On Friday, January 22, Dina Cheney sat down to enjoy a cinnamon raisin English muffin for breakfast at her home in Connecticut. The texture of the nooks and crannies was the same as always, but the muffin was completely flavorless. Knowing this could be a sign of COVID-19, the 43-year-old got a rapid test. The results confirmed her suspicion: She had the coronavirus.
For about five days, the cookbook author and chocolate-tasting host had virtually no sense of smell. Even foul odors were completely undetectable. This made sense, since our senses of smell and taste work together to let us perceive flavor. “I was quite disturbed, but also grateful that I wasn’t working on a cookbook or tasting project at the time,” Cheney says. “I remember thinking that if a project came up, I could rely on my memory for how much seasoning to use, but I would not have been able to detect and adjust subtle qualities.”
After seeing a few headlines about smell training, she decided to attempt it herself. “As I started, I did what I thought made sense,” she says. “I decided to concentrate while smelling the same strongly flavored items each day, to try to stimulate and help me pinpoint whether I was regaining my sense of smell.”
Once or twice a day, Cheney smelled a variety of items one at a time for a few seconds each: ketchup, mustard, miso, kimchi, coffee, cinnamon, a eucalyptus candle and lavender, cedar and sage essential oils. After about two weeks, her sense of smell seemed fully restored. “Each day after the first five days, aromas became stronger or less faint. I was able to derive enjoyment from them more and more each day,” she says. “I also began to detect unpleasant smells, like dirty laundry and bathroom odors. It was the first time I felt grateful to smell them.”
It’s hard to know if Cheney regained her sense of smell because of her training regimen, or if it naturally came back over time. But olfactory training doesn’t pose any health risks, and research suggests it can help restore smell loss caused by infections, including but not limited to COVID-19.
At a loss
Loss of smell, or anosmia, can be caused by health issues including viruses, head trauma, and neurodegeneration. With rhinoviruses (which cause the common cold), parainfluenza (which causes respiratory illnesses) and other flu viruses, scientists believe smell loss is usually caused by swelling and congestion, which block odor molecules from reaching receptors in the nose. “However, if the congestion clears and smell does not return, then it is likely that the virus has affected some part of the olfactory system,” says olfactory scientist Pam Dalton of the Monell Chemical Senses Center. She explains that the olfactory bulb — the structure in the brain that processes smells — shrinks from lack of stimulation when you “go without smelling for months or a year.”
COVID-19 may behave differently than other respiratory viruses, though. It appears to infect cells that deliver nutrients to the olfactory nerve so it can send messages to the brain about smell, says Jay Piccirillo, professor of otolaryngology at the Washington University School of Medicine. Compared to people who only lose smell temporarily, Piccirillo says those with lingering anosmia have “lost support long enough that they suffer irreversible damage, or the virus may invade the smell nerve.”
Whatever the cause, losing your sense of smell is disorienting. “People can’t even describe how lost they feel,” says Dalton. “Familiar places are no longer familiar because they don’t smell a certain way, and people you’re intimate with feel like strangers.”
A different kind of sniff test
Depending on the cause, smell loss can be temporary or long term. For example, an expert in a BMJ article reported that 90 percent of COVID-19 patients recover their smell with no assistance in two to three weeks. The rest may need months or even more than a year to fully recover — or they may never regain their sense of smell, based on what’s known about other instances of post-viral anosmia.
“The idea behind smell training,” Hummel explains, “is that the more you expose yourself to odors, the better your sense of smell is.” Consider chefs, perfumers and even parents — they all become acutely sensitive to certain, highly relevant scents. Taking a structured approach to fine-tuning your scent palate seems to amplify your ability to detect smells.
The process is simple: Twice a day, you sit in a quiet space and sniff specific odors. The standard protocol uses rose, lemon, clove and eucalyptus essential oils. Repeat daily for about four to six months.
Research suggests it works. In one 2009 study, 40 people with smell loss showed increased olfactory function after 12 weeks of smell training. Members of the control group, who didn’t train, didn’t see the same changes. More recently, meta-analyses from 2016 and 2017 concluded that olfactory training shows promise and should be considered as a smell-loss treatment method.
Although scientists don’t know exactly how olfactory training helps, one theory says stimulating the olfactory receptors “energizes” the brain’s smell pathways, bringing them back to life. This happens, the theory holds, even if someone can’t consciously perceive odors. “The brain is plastic; it can change,” says Piccirillo. “The idea is if you expose your nose to various odors, through that repetitive process, you can retrain the brain to recognize the smell.”
MRI scans suggest smell training increases volume in the olfactory bulb and brain regions involved in processing smell. It may also help those with parosmia, a distorted sense of smell that can make coffee smell like wet dog, or make different scented lotions smell exactly the same. With this issue, Dalton explains, “the axons of receptors in the nose that make connections to cells in the olfactory bulb have lost their mapping.” As a result, those axons connect to cells that belong to different smells. Basically, the wires between the nose and the brain are crossed.
Whiffs of the future
While Cheney fully regained her sense of smell, not everyone who tries training is so lucky. “Are people happy with what comes back? Most are,” says Thomas Hummel, a professor in the department of otorhinolaryngology at the Dresden University of Technology. “Do people reach a normal level or expected level when we measure it? Many do not.” For people with normal olfactory function who lose their sense of smell entirely, however, returning to an “in-between level” might not seem so bad. Timing is also a factor, says Dalton: It’s best to start the training early, do it regularly and stick with it for a few months.
With so many experiencing anosmia or parosmia due to COVID, researchers have more study subjects than ever, enabling more and deeper work on smell training. For example, Piccirillo is currently studying what happens when people are allowed to choose which scents to train in, as well as whether viewing pictures of scents during training enhances its impact. (He plans to do more studies, so if you are interested, you can join his anosmia registry.)
We may not think much about our sense of smell until we lose it. Fortunately, if you find yourself thrown off-balance by an odorless world, there’s more you can do than cross your fingers and hope to smell again. “With so many people losing their sense of smell and the effect this is having on their lives, we’re looking at recovery and going to learn a lot about this,” Dalton says. “We may have more effective treatments down the line.”