March 31, 2025
COLUMBUS, Ohio – Loss of smell. It was a common symptom for millions of people during the COVID-19 pandemic.
But it’s not the only condition that can alter the sense of smell. Sinus infections, head trauma, neurological diseases and aging can all cause problems with smell.
When you can’t smell, you also can’t taste and enjoy food. It affects your ability to detect dangers like gas, smoke or spoiled food. And there currently is no effective treatment for it.
To address this issue, researchers at The Ohio State University College of Medicine are the first in the world to design non-invasive smell aids that improve the ability to smell in healthy people and people who have difficulty smelling.
“For centuries, there have been innovations to help people see and hear better, but there haven’t been worthwhile methods that improve olfactory function or the ability to smell,” said Kai Zhao, PhD, professor in the Department of Otolaryngology – Head and Neck Cancer. “The smell aids our team developed hold the promise of becoming effective, over-the-counter therapies like eyeglasses and hearing aids.”
The clinical trial tested the use of two smell aid prototypes that increase the flow of air to the tissue in the nasal cavity responsible for the sense of smell. A nasal foam plug made from ear plugs redirects air and odor flow to this region. A nasal clip, similar to those used by synchronized swimmers, pinches a nasal valve area that intensifies nasal airflow to the same area.
Fifty-eight healthy people and 54 patients with smell deficits participated in the trial. Of the patients with smell deficits, 69% suffered from post-COVID olfactory dysfunction. The remaining had loss or distorted sense of smell due to head trauma, head and neck cancer and surgery, or nasal polyps.
During smell tests in healthy people, participants squeeze and sniff two bottles one after the other and must identify which bottle contains the odor. The patients with smell deficits complete testing using the National Institutes of Health odor identification test, which includes 9 scratch and sniff odor ID cards. The patients scratch and sniff each of the 9 cards in random order and select the odor based on 4 multiple choices. Both groups completed the testing at baseline and while wearing the nasal plug and the nasal clip, in counter-balanced order.
In healthy study participants, odor detection significantly improved with both prototypes in people with normal smell function but not in people with a super sensitive sense of smell.
“This probably makes senses—as an analogy, eyeglasses may significantly improve suboptimal vision, but have little effect on perfect 20/20 vision,” Zhao said. “And the improvement is quite robust with an effect size of 2.1 (95%CI: 0.334 -3.797). Since these odor bottles are prepared in semi-log dilution, this means that those people detect the odor at over 10 times lower in concentration after putting on the smell aids.”
Among patients with smell loss, the NIH toolbox odor ID score improved after using both smell aids, especially in the non-COVID group, with an effect size of 1.065 (95% CI: 0.190-1.940).
“These patients can detect and correctly identify on average one more odor, after wearing the smell aids”, Zhao said. “For COVID long haulers, only the nasal plug remains effective.”
The study results demonstrate the ability to improve the sense of smell with non-invasive devices in different types of users. There currently are no effective targeted therapies for long-term olfactory dysfunction. Existing treatments for smell loss such as olfactory training and platelet-rich plasma injections are supportive or experimental.
“The smell aids have the potential to broadly help people who have olfactory loss or depend on smell for their careers like chefs, perfumers and food and wine critics, and people who want to enrich the experience of enjoying food and fragrances,” Zhao said.
Future research will focus on refining the design and improving the effectiveness of the smell aids.
The article, “Designing novel “Smell-Aids” to improve olfactory function in post COVID-19 era,” is published in the journal BMC Medicine. Additional Ohio State authors include Veronica L. Formanek, Barak M. Spector, Gabriela Zappitelli, and Zhenxing Wu, PhD.
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Media Contact: Serena Smith, Wexner Medical Center Media Relations, Serena.Smith@osumc.edu