DIY smell tests at home can detect cases of Covid-19

DIY smell tests at home can detect cases of Covid-19

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In early October, one of our undergraduate students told her mother’s story and her daily coffee routine. It perfectly illustrates how scent checks can be used as a screening tool for Covid-19 infection. One afternoon, the mother of our graduate student went to prepare her usual cup of coffee and found that she couldn’t smell or taste it. She had heard from her daughter about anosmia associated with Covid, so she tried to smell a pine-scented cleaning spray, but she also couldn’t smell it.

Due to her sudden and inexplicable anosmia, our student’s mother was quarantined and tested Covid-19, which was positive. Taking her loss of smell seriously, doing a quick, self-insulating test, she created a dead end for the virus, breaking the chain of transmission before the virus could spread to someone else.

According to some estimates, 44% to 77% of people with Covid-19 lose their sense of smell. But many are unaware that they have lost their sense of smell until they actively try to smell something that should have an odor, like scented candles. That’s why we encourage people to actively try to smell something every day. Sudden unexplained anosmia is a specific symptom of Covid-19. It can be used as a daily DIY screening tool by individuals, providing another tool in the struggle to contain Covid-19.

A scent stopper

Covid-19 affects your sense of smell in a different way than a common cold. When the nose is clogged, odors – active, light-smelling molecules found in the air – are physically unable to reach the smell receptors at the top of the nasal cavity.

With Covid-19, the loss of smell is caused by an interruption of signaling. Research has shown that the virus attacks cells behind the bridge of the nose immediately next to olfactory neurons. These support cells are covered by many of the ACE2 receptors that the virus exploits to enter cells, so they are especially vulnerable. This tissue becomes inflamed, temporarily disrupting the ability of olfactory neurons to signal the presence of an odorant.
Unlike the common cold, many patients with Covid-19 also lose their taste and also their chemesthesia – the ability to feel the tingling of carbonation or the burning of chili peppers.
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A very specific symptom

Unexplained anosmia is usually very rare with other viral infections, especially in the absence of nasal congestion or obstruction. If someone loses their sense of smell, it is a good sign of a possible Covid-19 infection. In fact, recent analysis suggests that if you had to choose just one symptom, sudden loss of smell may be the best predictor of a Covid-19 diagnosis.
Loss of smell is very specific for Covid-19, but not everyone with SARS-CoV-2 infection reports loss of smell. Critically, being able to smell things doesn’t mean you’re free from Covid. If you were able to smell your coffee this morning, this is an ambiguous result: it may mean that you don’t have Covid-19, but it can also mean that you are infected with SARS-CoV-2 and you just haven’t lost your normal sense of smell.

Although fever tests have been widely implemented, they are not specific to Covid-19 – many other illnesses, like flu or strep throat, also cause fevers. Using smell loss as a Covid-19 test is far from perfect. But since a daily odor check is very specific, instant and literally free, it is a highly useful screening tool.

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Do it yourself, daily

The story of our graduate student’s mother illustrates how active smell checks can detect cases of Covid-19 in people without other symptoms. At Penn State, where we work, we are putting this into action.

This fall, the school launched our “Stop. Smell. Be well” project to raise awareness about the connection between the sudden loss of smell and Covid-19. We even developed different “sniff cards” with a peel and smell panel so that people could check their sense of smell with a standard tool.

Although this tool is preferable for research, doing a daily smell test for public health reasons does not require a personalized smell card. The test can be simply smelling your cup of coffee in the morning or the shampoo you use in the shower.

Smells cannot and will not detect all undiagnosed infections, since about a quarter to half of Covid-19 patients do not lose their sense of smell. But, since DIY scent tests can be done at zero cost, the disadvantages of using them for screening are minimal.
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Screening stops spreading

Screening is one of the most basic public health tools. The most critical factors for an effective Covid-19 screening tool are frequency and speed, with test sensitivity being secondary.

It’s easy to check your nose – who doesn’t have a bag of coffee or tea in the kitchen or a bar of soap in the bathroom? And it’s quick – you know immediately if the milk has gone sour. Combine this with the high specificity of anosmia in relation to other symptoms, and we believe that daily smell checks at home can help fill the need for a fast, inexpensive and specific screening tool. Tracking sudden smell loss can even be used to monitor cases of Covid-19 at the population level in a country or region.

Obviously, no screening program will detect 100% of cases. It is essential that individuals continue to practice other harm reduction behaviors. Still, we encourage you to stop. Smell. Be alright. And if you lose your sense of smell, isolate yourself and contact a health professional.

The conversation

John E. Hayes is a professor of food science at Penn State. Cara Exten is an assistant professor of epidemiology at Penn State.

Disclosure: John E Hayes received research funding from federal agencies (USDA, NIH), state agencies (PA Dept of Ag) and commodity groups (PA Wine Marketing Research Board, The Sugar Association). He accepted travel expenses and lecture fees from nonprofit organizations (ILSI North America), food companies (Kerry Group, Hershey Company) and the federal government (FDA). He consulted with the federal government (FDA) and food companies (Heineken, General Mills, PepsiCo) on flavor perception. He serves as Section Editor for the journal Physiology & Behavior. Its laboratory, the Penn State Sensory Assessment Center, also conducts routine taste tests for industrial customers to provide experimental learning for undergraduate and graduate students. External proposals for funding research related to Covid-19 are currently pending.

Cara Exten receives funding from federal (NIH) and state (PA Department of Health) agencies. She is on the AIDS Resource Alliance Board of Directors. External proposals for funding research related to Covid-19 are currently pending.

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