Could 'Scratch-and-Sniff' COVID-19 Testing Work?

A Black woman wearing a red shirt smelling a fresh cup of black coffee.


Although COVID-19 vaccines are rolling out in the United States, the country is still a long way off from eradicating the virus. Lack of adequate testing continues to be a concern, especially in rural areas. Scientists around the world are hoping to develop more efficient and accurate ways to test for COVID-19.

A recently approved two-year study will investigate how scratch-and-sniff testing could become an affordable and accessible testing methodology. The research will be a joint project between Penn State, the University of Florida, and Arizona State University. It will be funded by the Coronavirus Aid, Relief, and Economic Security (CARES) Act and the National Institute of Health (NIH).

COVID-19 and Sense of Smell

John Hayes, PhD, lead researcher for the upcoming study and a professor of Food Science at Pennsylvania State University, tells Verywell that loss of smell is a unique symptom of early COVID-19 infection.

"With the normal common cold, you often lose things, 'things don't taste right.' That's because there is confusion in English between smell, taste, and flavor and how we define those terms scientifically versus how the average person uses them," Hayes says. "They don't align perfectly. When you have a classic cold, you're literally plugged up so that nothing will flow through your nose."

Unlike when you have a cold, COVID-19 smell loss happens with little to no congestion or physical blockages.

The sensory deficiency and accompanying loss of taste (because taste and smell are intrinsically linked), is one of the only symptoms of COVID-19 that is unique. Other early-onset symptoms like fever, cough, or body aches can be symptoms of many illnesses or viruses from allergies to food poisoning.

The AE2 Receptor

While research on the connection between smell and COVID-19 is ongoing, David Brand, a graduate student at Harvard University and member of the Datta Lab, found a link between ACE2 receptors and the supporting sustentacular cells that could be key to unraveling the cause.

"The ACE2 receptor is the keyhole that the virus uses to stick..." Hayes says. "[It] inserts the spike protein into it and uses it to get inside the cell."

Hayes explains that the ACE2 receptor is heavily expressed in some cells at the top of the nasal cavity. "It doesn't actually seem to disrupt the smell receptor cells themselves," he says. "There are these supporting cells that live immediately next door."

Smell receptors are expressed on olfactory sensory neurons (OSN), which are right next to sustentacular cells. "It turns out that the OSN themselves don't have a lot of ACE2 receptors on them, but the sustentacular cells do," Hayes says. "So, the current working hypothesis is that the virus attacks these cells and causes a local perturbation, local inflammation at the very top of the nasal cavity, that temporarily disrupts the sense of smell."

ACE2 and COVID-19

The attack on the sustentacular cells also explains why the loss of smell is such a sudden onset for people with COVID-19—there's no build-up of a physical blockage to create conductive smell loss, as with the congestion of a cold. Instead, it's the ACE2 receptor interrupting the function of the supporting structure of the olfactory senses.

How the Test Could Work

The study aims to launch field testing in mid-January. It will gather information on two tests. One will use an abbreviated version of the University of Pennsylvania Smell Identification Test (UPSIT), and the other will use different concentrations of smells to determine the lowest concentration that participants can smell.

The researchers hope to figure out which test is a better predictor of COVID-19 infection by the end of the study.

While the loss of smell is unique to COVID-19, it's not a guaranteed symptom of the infection. Current estimations show that between 45% and 75% of confirmed COVID-19 positive cases describe experiencing loss of smell.

Hayes and his co-researchers, Steven Munger, director of the University of Florida's Center for Smell and Taste, and Cara Exten, assistant professor of nursing at Penn State, will be creating an ethnically and racially diverse population of participants for the study, pulling from north Florida, Arizona, and Pennsylvania, as well as another site in the upper midwest.

While there would be false negatives using smell tests alone, Hayes says that the ability to easily and affordably test large groups, such as schools and businesses, would still be advantageous.

A Longterm Testing Solution?

The study has a two-year run time, which opens up the question of whether vaccine rollouts will make the outcomes irrelevant. Hayes hopes so but still sees significant value to the information to be gleaned from the research.

"Even once the vaccine rolls out, even if we can knock the baseline rates down, we're still going to local hotspots," he says, "For that, smell testing might be really great."

Hayes gives the example of a liberal arts college in a small town with a small regional hospital. "You have 5,000 undergraduates, and then all of a sudden you have an outbreak, your ability to test every student to then quarantine is still going to be really resource-intensive," he says. "But if you can give all 5,000 students a pack with 14 days worth of scratch and sniff cards, then you could use that."

A lack of resources and the cost of testing are problems that continue to challenge communities worldwide. Even with adequate funding for vaccine rollout, current estimates show that we might not reach global inoculation levels until 2023 or 2024.

While it is not a for-sure indicator, analyzing your own sense of smell is easily accessible and free. Hayes says that a daily smell test at home can be a valuable tool for many people. Simply checking whether you can smell your morning coffee, your pet, or your partner can be a valuable indicator of early-onset COVID-19 infection.

What This Means For You

Losing your sense of smell is one of the most unique symptoms of COVID-19. If you're experiencing a loss of sense of smell without any accompanying physical blockage such as congestion, you might want to get a COVID-19 test.

That said, losing your sense of smell is not a for-sure sign that you have COVID-19—and you can still have COVID and your sense of smell. If you have not lost your sense of smell but have a fever, cough, or body aches, ask your healthcare provider if you should get tested for COVID-19.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Penn State University. Researchers investigate an at-home “scratch-and-sniff” test for COVID-19.

  2. Brann DH, Tsukahara T, Weinreb C, Lipovsek M, Van der Berge K, Gong B, et al. Non-neuronal expression of SARS-CoV-2 entry genes in the olfactory system suggests mechanisms underlying COVID-19-associated anosmiaScience Advances. 2020;6(31):eabc5801.

  3. McDonnell A, Van Exan R, Lloyd S, et al. COVID-19 Vaccine Predictions: Using Mathematical Modelling and Expert Opinions to Estimate Timelines and Probabilities of Success of COVID-19 Vaccines. Center for Global Development.

By Rachel Murphy
Rachel Murphy is a Kansas City, MO, journalist with more than 10 years of experience.