About 1 in 15 Americans over the age of 40 smells “phantom odors” — often something unpleasant, like rotting food — when nothing is actually there, according to a study published in JAMA Otolaryngology-Head and Neck Surgery.
Although the phenomenon of perceiving phantom odors has long been acknowledged in the medical community, it hasn’t been well studied. The current study, which was conducted by researchers at the National Institute on Deafness and Communications Disorders (NIDCD), is apparently the first to take a close look at how common the mysterious condition is in the United States and who is most at risk.
The research is not being driven by idle curiosity. The condition — known medically as phantosmia — can have health-related consequences.
“Problems with the sense of smell are often overlooked, despite their importance,” said Judith Cooper, the NIDCD’s acting director, in a press release. “They can have a big impact on appetite, food preferences and the ability to smell danger signals such as fire, gas leaks and spoiled food.”
Such conditions can also affect people’s quality of life. People with persistent phantosmia often report a “miserable” quality of life and sometimes have trouble maintaining a healthy weight, said Dr. Donald Leopold, the study’s senior author and an otolaryngologist at the University of Vermont, in the same press release.
Scientists don’t know what causes phantosmia in otherwise healthy people, although it may be some kind of neural signaling imbalance, according to background information in the study. That imbalance may result from damage to the olfactory sensory neurons, which are found at the back of the nose. Or it may be due to some kind of damage to areas in the brain where odors are processed.
A matter of age
For the study, Leopold and his colleagues used data collected from 7,415 participants in the 2011-2014 National Health and Nutrition Examination Survey (NHANES). All were aged 40 or older.
One of the questions on the survey asked people if they “sometimes smell an unpleasant, bad, or burning odor when nothing is there.” (Most people describe phantom odors as burnt, foul, spoiled, rotten or otherwise unpleasant, although occasionally the odors are reported as being neutral or pleasant.)
The study found that 6.5 percent of the respondents — 534 individuals — answered that question with a “yes.” The proportion dropped with age however — to 5.4 percent among those aged 60 and older.
That age difference may be because people lose olfactory sensory neurons — including, perhaps, some of the damaged one that cause phantosmia — as they grow older, according to the study’s authors.
Other risk factors
The researchers then took a deeper dive into the data to see what other factors might be associated with the condition. They found that the risk of perceiving phantom odors was twice as high among women as among men, particularly before the age of 60. The reasons for this gender difference are unknown.
The study also found that blacks and Hispanics were more likely to report phantom odors than whites. “However, when we accounted for the greater prevalence of phantom odors among people of lower socioeconomic position, we observed no difference across race/ethnic groups,” the researchers write.
Why are phantom odors more common among people of lower socioeconomic status? It may be because they have health conditions that contribute to the problem or because they live in communities where they’re at greater risk of exposure to air pollutants and other environmental toxins that can damage olfactory neurons, say the researchers.
It may also be because poorer people are at greater risk of head injuries. The current study found that a history of trauma to the brain was a strong risk factor for phantom odors.
Interestingly, people who had a history of an injury to the nose, face or skull were not more likely to have phantosmia. Another risk factor uncovered in the data was dry mouth, or xerostomia, a condition in which the salivary glands in the mouth make insufficient saliva to keep the mouth moist. People with dry mouth were three times more likely to report perceptions of phantom odors than those without dry mouth.
This may be because of the medications they take for the condition, the researchers point out.
The study found no association between how well people scored on “smell tests” and phantosmia. In other words, people with the condition do not just have more sensitive noses.
Not well understood
The study is observational, so it can’t prove a direct causal relationship between any of the identified risk factors and phantosmia. Also, the data used in the study didn’t provide information on the intensity, duration or frequency of the phantom odors.
Still, the study is a start on understanding a little-known condition that appears to affect the quality of life of a significant number of Americans.
“The causes of phantom odor perception are not understood,” said Kathleen Bainbridge, the study’s lead author and an epidemiologist at NIDCD, in the press release.
“A good first step in understanding any medical condition is a clear description of the phenomenon,” she added. “From there, other researchers may form ideas about where to look further for possible causes and ultimately for ways to prevent or treat the condition.”
FMI: You’ll find an abstract of the study at the JAMA Otolaryngology-Head and Neck Surgery website, but the full study is behind a paywall.