Phantom odor perception (POP) describes the experience of smelling something — perhaps burning hair or an ashtray — that is not there.
This experience is well documented, but very little specific research has been carried out.
Scientists of the Epidemiology and Biostatistics Program at the National Institute on Deafness and Other Communication Disorders (NIDCD) recently conducted a study into POP, asking why it might occur in certain people but not others.
Kathleen Bainbridge, Ph.D., led the study. Its findings are now published in JAMA Otolaryngology—Head and Neck Surgery.
Researcher Judith A. Cooper, Ph.D., the acting director of the NIDCD, explains why this topic is important.
"Problems with the sense of smell are often overlooked," she says, "despite their importance. 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."
The statistics behind POP
The researchers took data from the National Health and Nutrition Examination Survey. They used data from more than 7,000 people over 40 years old, taken in 2011–2014.
Within the questionnaire was the question, "Do you sometimes smell an unpleasant, bad, or burning odor when nothing is there?"
They discovered that, overall, 6.5 percent of people over the age of 40 experienced POP, which equates to around 1 in 15 people.
Sense of smell tends to decline with age, but the opposite seemed to be the case for POP. Around 5 percent of over 60s experienced the phenomenon, but the figure was much higher in the 40–60 age range.
The study also revealed that POP affected women almost twice as often as it did men, and this sex difference was more pronounced in the 40–60 age group.
When the scientists looked for potential risk factors, they found that risk was increased for people with poor overall health or a lower socioeconomic status.
This latter risk factor, they hypothesized, could be because people with a lower socioeconomic status might be exposed to higher levels of environmental pollutants and toxins. They are also more likely to have other health conditions and medications that could produce POP.
Head injury, smoking, and alcohol
Those with dry mouth had three times the risk of those who did not. Head injuries increased risk, too; 1 in 10 people who had experienced a loss of consciousness due to a head injury reported POP. However, injury to the face, nose, or skull without a loss of consciousness did not affect people's risk.
Furthermore, individuals who smoked cigarettes regularly were more likely to report POP. Overall alcohol consumption was not related to POP, but those who drank alcohol on more than 3 days each week had a lower risk.
"The causes of phantom odor perception are not understood. The condition could be related to overactive odor-sensing cells in the nasal cavity or perhaps a malfunction in the part of the brain that understands odor signals."
Kathleen Bainbridge, Ph.D.
She continues, "A good first step in understanding any medical condition is a clear description of the phenomenon. 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."
This is the first time that POP has been quantified in the United States population and adds to our understanding. The condition has proved difficult to quantify in the past because people do not necessarily mention it to their clinician. In this sample, for instance, only 11.1 percent of those experiencing POP had discussed it with a medical professional.
Hopefully, a greater awareness of the condition might help provide clearer answers in the near future.