Katie Boateng was eating breakfast when she realized something was wrong. Her roommate, in a cleaning fervor, was spraying bleach around the kitchen, but Katie couldn’t smell a thing. She started sniffing everything, from leftovers in the fridge to the trash can. Nothing. 

Many tests followed: endoscopy, a CT scan, an MRI. Six months later, Boateng got a diagnosis: postviral anosmia, a complete loss of the sense of smell. Most likely a cold virus, just a few weeks before the bleach incident, had destroyed her olfaction. 

That was 17 years ago. “I’ll never know what my son smells like,” she says. She still has reason for hope despite the lack of a cure for postviral anosmia. New therapies are emerging, from injections of platelet-rich plasma to electrical stimulation of the vagus nerve. 

Before the COVID-19 pandemic, more than 13 million Americans, or about 1 in 8 over the age of 40, had a measurable smell dysfunction, caused by anything from viral infections to seasonal allergies, head trauma, neurodegenerative diseases, or simple aging. COVID-19 was a game-changer: It left more than half of those infected with a smell disorder, according to early estimates. For most, smell came back within weeks, though for some smell dysfunction lasted months or even years. 

There is a range of severity in anosmia. Some people, such as Boateng, completely lose their sense of smell after a viral infection, be it COVID-19, flu, or a simple cold. Others have reduced olfactory function but can still pick up some scents. Some have distorted olfactory sensations, or parosmia: A rose might smell like garlic. “Their food smells like feces or dirty socks, or some terrible toxic chemical,” said Zara Patel, MD, an otolaryngologist at Stanford University in Stanford, California. Up to 35% of people with olfactory disorders have parosmia; that number can reach 45% among those recovering from COVID-19. 

Smell is “not one of the senses that really jumps to the top of your list of importance — until you lose it,” said Eric Holbrook, MD, MS, an otolaryngologist at Harvard Medical School in Boston.

Smell dysfunction can be dangerous. People with impaired olfaction are three times more likely than others to start a fire while cooking, or fail to notice a gas leak. Many end up eating spoiled food.They worry about their body odor and say they enjoy sex less. About a third of people with anosmia suffer from depression. 

Smell loss during the COVID-19 pandemic led many to seek treatment, and dubious remedies proliferated on social media (eg, smelling burnt oranges). Heightened interest led to more studies, many of which were poorly designed, Patel said. Because smell function tends to regenerate on its own, a placebo control is needed to study the efficacy of a treatment — but that often didn’t happen, she said. 

Current research reveals little support for corticosteroids or vitamin supplements, but some approaches show promise: olfactory training, platelet-rich plasma, and electrical stimulation. Here’s where the research stands.

Corticosteroids and Oral Options

Verdict: ineffective

The pandemic caused a resurgence in steroid treatment, Holbrook said. Such therapy seemed to make sense because corticosteroids have anti-inflammatory properties, and inflammation is one of the proposed mechanisms of how viruses damage the sense of smell. But a 2022 Cochrane review found no evidence that corticosteroids help with persistent post-COVID-19 smell troubles. A 2025 review of four studies, including two randomized controlled trials, showed no effects of oral corticosteroids on olfactory function, either. Patel said she doesn’t prescribe oral steroids: “I think that’s a waste of time and puts people at risk for no reason.” 

Steroid sprays don’t seem to be much better. The 2025 review analyzed five studies on the use of topical corticosteroids and found inconsistent results with no statistical significance. “That makes total sense, because sprays are not going to be able to reach the olfactory cleft,” Patel said. The olfactory cleft is a thin slit at the top of the nasal cavity where scent molecules activate odor receptors nestled within the olfactory epithelium. If the corticosteroids don’t make it all the way up there, they are unlikely to have a real impact.

Several other oral remedies found no research support, either. That includes vitamin A supplements as well as palmitoylethanolamide and luteolin, touted for their anti-inflammatory properties. Intranasal vitamin A did better under scrutiny, but according to a 2023 review, the evidence is still weak. Psychedelics are also making rounds on social media as a cure for olfactory dysfunction, yet so far there appear to be no studies evaluating whether LSD or psilocybin can truly help people struggling with their sense of smell. 

Olfactory Training

Verdict: limited success

Olfactory training was proposed in 2009 by Thomas Hummel, MD, a neuroscientist at the University of Dresden Medical School, Germany, and his colleagues. The idea was simple. Twice a day, a group of patients with smell dysfunction took deep, 10-second-long inhalations of four strong aromas: rose, clover, lemon, and eucalyptus. A control group simply waited for their sense of smell to improve on its own. After 12 weeks, the ability to detect scents significantly increased in the aroma group — which didn’t happen for those in the wait-and-see group. “It’s not like an earth–shattering thing; the regeneration is limited, but you can improve it,” Hummel said. 

Subsequent trials concurred. A 2020 meta-analysis of 16 studies found that olfactory training offered patients significant improvement, and so did a 2023 meta-analysis of studies on post-COVID-19 olfactory disorders. Hope was tempered by a 2025 randomized controlled trial that found patients with smell issues caused by COVID-19 were no better after a 12-week olfactory training than a control group that sniffed an odorless placebo. Hummel notes that the null results could be explained by delayed treatment: Most of the study participants had been struggling with olfactory dysfunction for more than a year, and the longer you wait with treatment, the harder it is to regenerate the sense of smell.

What’s more, 12 weeks may not be enough. Ideally, Hummel said, training should occur twice a day for 4-6 months. Three out of four people give up during the first 4 weeks, a survey found. “It’s very boring,” he said.

Olfactory training appears to boost the recovery of olfactory neurons and the receptors they carry, which may have been damaged by a virus, Hummel said. “It amplifies regular regeneration.” Our sense of smell works on a use-it-or-lose-it basis. Studies show that neurons disappear from the olfactory epithelium if they are not stimulated by odors. This may explain why people who work in completely odorless environments, such as cleanrooms for making microchips, often end up with a less sensitive nose.

In Hummel’s experience, fewer than half of patients in training will notice improvement. There may be ways to up this success rate. Humans have about 400 olfactory receptors, but the scents traditionally used for olfactory training stimulate fewer than 40% of them. To find a better mixture, Holbrook and his colleagues analyzed complex data on odors and the receptors each of them stimulates. The two aromas best suited for training proved to be not roses and lemons, which are typically used, but galaxolide, a synthetic musk scent, and geranyl acetate, a floral aroma. In a similar study published in December 2025 by researchers in France, the top scents proved to be galaxolide and benzothiazole, which smells like meat. The two teams are now working together to create a clinically relevant set of aromas for olfactory training 2.0, Holbrook said. 

Platelet-Rich Plasma

Verdict: some promise

Platelet-rich plasma (PRP) is particularly promising for people whose smell has been damaged by a virus. PRP is obtained by spinning a sample of a patient’s blood in a centrifuge, which concentrates platelets in the plasma — cell fragments that release growth factors and help stimulate tissue repair. A 2022 randomized controlled trial by Patel and her colleagues showed that for COVID-19 patients with smell dysfunction, three PRP injections into the olfactory cleft meant “a greater than 12 times odds of improving smell,” compared to placebo, Patel said. Her 2024 follow-up study showed that PRP continued to improve olfaction for months after the initial injections.

Holbrook is unconvinced. “I’d like to see larger well-controlled clinical trials showing benefit before considering offering this to my patients,” he said. Patel is running another randomized controlled trial to check if PRP could help in parosmia. For now, however, costs are a big issue for patients, because the therapy is expensive and not yet reimbursed.

Electrical Stimulation

Verdict: success for some

Patel said she is excited about electrical stimulation. For a 2025 Italian study, patients who had had COVID-19 underwent 10 sessions combining olfactory training with transcranial stimulation. They wore a fabric cap on their heads that secured an electrode delivering a mild current to the prefrontal cortex. These were people for whom steroids, supplements, or training hadn’t seemed to work. But after 2 weeks of transcranial stimulation, 63% achieved complete recovery. In the control group, which received only sham stimulation, such improvements didn’t happen. 

Hummel and his colleagues published results of a similar trial in October 2025. An electrode was attached to the patient’s left ear to stimulate the vagus nerve, which can influence how smells are processed. For some, the gains were so dramatic that they asked Hummel to sell them the device so they could “use it before meals,” he said. While for most patients the changes weren’t “super strong,” Hummel said, they were still “promising.” He is currently running a follow-up study with a larger group. 

Stem Cells and Implants

Verdict: future hope

Work is ongoing with neural stem cells, which have recently been shown to boost the sense of smell in mice. Several researchers, Hummel included, are also working on olfactory implants that could stimulate brain regions responsible for smell. While it’s still early days for such implants, and many challenges remain (including how to make them tiny), Hummel remains optimistic: “I don’t know when exactly, but it will come,” he said.

In the meantime, people with olfactory dysfunction shouldn’t wait to try something. “The longer you go, the less likely you are to benefit from anything,” Patel said. Besides olfactory training and PRP, try surrounding yourself with scents. Research shows that people who train to become sommeliers (wine experts) experience growth in olfactory bulb volume and also become better at identifying aromas. Something similar happens in people working in perfumeries. “The more odors you bring into your daily life,” Hummel said, “the better your sense of smell will be.”