The loss of taste and smell that accompanied early COVID infections may have seemed like a novelty to those who weren’t afflicted.

But it wasn’t for the millions of patients who experienced the bizarre symptoms—and many still are. Nearly two-thirds of Americans infected with COVID since the beginning of the pandemic partially or completely lost their sense of smell and/or taste, researchers estimate in an article published this month in the journal The Laryngoscope.

While the majority regained their senses, nearly 6 million Americans may still be coping lingering symptoms, Dr. Neil Bhattacharyya, a professor of otolaryngology at the Harvard University-affiliated Mass Eye Ear and an author on the study, told Fortune.

“Many people never fully recovered,” Bhattacharyya said.

The study examined data from nearly 30,000 U.S. adults who were surveyed about their COVID symptoms in 2021. After participants recovered from their acute infection, nearly three-quarters reported regaining their sense of smell. But nearly 24% didn’t fully recover it, and more than 3% didn’t recover any sense of smell by the end of 2021, researchers found. The numbers looked similar when it came to recovery of taste (or lack thereof).

Researchers also noted that the more severe a patient’s COVID symptoms, the more likely they were to lose their sense of taste and/or smell—and the less likely they were to recover them.

The impact on daily life

Early in the pandemic, focus was placed on the lost of taste and/or smell as a novel diagnostic criteria for COVID.

“But we forgot a little bit that the symptoms are still an affliction on the back end,” Bhattacharyya said. “If you lost your sense of smell, did you get it back? There’s about a one in four chance you didn’t. That’s terrible.”

And the symptoms aren’t “as benign as you may think,” he added. They can “lead to decreased eating for pleasure and, in more extreme cases, it can lead to depression and weight loss.”

Those who suffer such sensory dysfunction can’t fully enjoy food, resulting in a reduced quality of life. And they may not be able to detect smells from gas leaks, smoke, rotten food, and other potential dangers. For those involved in the culinary industry, like chefs and sommeliers, the disability even interferes with work.

One of Bhattacharyya’s patients lost 50 pounds due to his COVID-induced loss of smell.

“The patient wasn’t eating and became very sick and very depressed,” he said. Without such senses, “food doesn’t taste good. The classic thing patients tell me is that food tastes like cardboard.”

What to do if you’re experiencing symptoms

As the world emerges from the fog of the pandemic, an increasing number of patients are showing up in Bhattacharyya’s office complaining that they can’t smell or taste—at least not fully.

“Many thought it would get better on its own,” and a year later, it hasn’t, he said.

Researchers still have many unanswered questions, including just how and why COVID affects the senses of some but not others, and when patients can expect to fully regain their senses, if at all.

When patients do recover, it’s not on a predictable timeline, Bhattacharyya said. It seems that the longer a patient’s symptoms last, the less likely it is that they’ll recover, he added.

Right now, there isn’t a standard treatment for the affliction, Bhattacharyya said, referring to affected patients as “a group of people who have been a bit neglected.”

He encourages those with symptoms to report them to their primary care provider, who will likely refer them to an ENT—or ear, nose, and throat—doctor. Another condition—perhaps a treatable one, like chronic sinusitis with polyps—could be to blame, he said. If not, they’ll be on the radar, should a treatment become avaliable down the road.

How to protect your senses from COVID

The study bolsters the case for getting the COVID vaccine and taking antiviral Paxlovid if your provider recommends it, as both have the potential to reduce the severity of COVID symptoms, the study’s authors wrote.

The good news for those who haven’t yet been affected: As the virus has evolved, so have the symptoms. Loss of taste and smell are no longer common among COVID patients, the Harvard and Stanford universities-backed Zoe Health Study reported late last year.