Traffic Pollution May Be Stealing Your Sense of Smell

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Jun 6, 2025 - 09:58 Updated: Jun 5, 2025 - 16:44
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Traffic Pollution May Be Stealing Your Sense of Smell
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If you’ve noticed that your morning coffee no longer smells as rich as it once did, or that the scent of fresh flowers has become harder to detect, traffic pollution may be to blame.

Recent research shows that living in areas with heavy traffic fumes is linked to a significantly higher risk of losing your sense of smell, which can serve as an early warning sign of brain damage or neurological issues.
The findings suggest that long-term exposure to exhaust fumes and fine particles from vehicle emissions can damage odor-detecting cells in your nose, and that these pollutants can travel directly into your brain, potentially contributing to the development of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
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Focus on Traffic-Related Pollutants

The new German study, recently published in Environment International, found evidence that prolonged exposure to traffic-related air pollution may impair our ability to identify odors.

The research, involving more than 3,000 middle-aged and older adults, tested participants’ ability to identify common scents like peppermint, coffee, fish, and lemon using a standardized smell test. Those scoring below 10 out of 12 were classified as having impaired smell (hyposmia) or no smell (anosmia), while scores of 10 or higher indicated normal function.

Researchers estimated long-term exposure to various air pollutants at participants’ residential addresses using land-use regression models based on data from 2014 to 2015.

They focused on several traffic-related pollutants, including particle number concentration (PNC), PM2.5 (fine particles), PM2.5 absorbance (a marker linked to vehicle emissions), PMcoarse (particles between 2.5 and 10 micrometers), PM10 (larger particle pollution), nitrogen dioxide, and nitrogen oxides (NOx). These air contaminants have been linked to respiratory and cardiovascular problems, premature death, and other adverse health outcomes, particularly for people with compromised immune systems.

“Exposure to traffic air pollution is definitely a significant health issue,” said Jenni Brandon, an environmental scientist and sustainability consultant at Wild Beacon Consulting, who was not involved in the study. “Most of the PM2.5 pollution found in outdoor air comes from combustion of gasoline, oil, and diesel fuel, so it matters more in high-traffic areas.”
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Significant Risk Increases Found

The findings indicate that higher concentrations of all pollutants were associated with increased odds of an impaired sense of smell.

For every meaningful increase in pollution levels, people were 10 percent to 20 percent more likely to have smell problems, depending on the type of pollutant. The worst offenders were coarse particles—dust-sized pollution from traffic—PM10, and black carbon, which is soot from exhaust.

These associations remained even after researchers adjusted for factors including age, sex, socioeconomic status, education, income, lifestyle behaviors such as smoking, physical activity, and alcohol consumption, and health conditions such as allergies, hypertension, and respiratory diseases.

Brandon explained that PM10—particles that are 10 micrometers or smaller in diameter—includes solids and liquids in that size class. Examples include dust from construction sites, landfills and agriculture, wildfires, and brush or waste burning.
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A Pathway to the Brain

According to researchers, air pollutants can penetrate the protective blood-brain barrier by compromising our olfactory barrier, which separates the bloodstream from the sensory cells in the nasal cavity.

These microscopic particles and gases can then travel directly along nerve pathways from the nose to the brain’s smell-processing center, the olfactory bulb. Once there, they can cause inflammation and cellular damage that may extend beyond smell function.

“These findings suggest a potential link between prolonged air pollution exposure and early changes in the olfactory system and could be indicative of early signs of detrimental effects on the brain,” the study authors wrote.

Researchers also highlighted a potential link they found between prolonged air pollution exposure and early neurodegeneration, such as Alzheimer’s and Parkinson’s disease. This is because particles such as PM2.5 and ultrafine particles can accumulate in the olfactory bulb or travel along the nerve to the brain, potentially causing inflammation and neuronal damage.

Dr. Austin Perlmutter, a board-certified internal medicine physician not involved in the research, noted that traffic-related air pollution (TRAP) is already a known risk factor for respiratory issues, heart disease, diabetes, depression, and dementia.

“This appears to be in part because TRAP leads to oxidative stress, inflammation, and metabolic dysfunction,” Perlmutter said. “TRAP is absolutely a significant health issue.” The study also found that women and physically active people appeared more susceptible to pollution-related olfactory impairment. Women had higher odds of smell impairment associated with pollutants like PNC, PM2.5, and NOx compared to men, though researchers aren’t yet sure why.

The increased vulnerability among physically active people may be due to increased breathing rate and depth during exercise, which may allow more pollutants to reach olfactory receptors.
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Protecting Yourself

Perlmutter said there are many practical tools that can help mitigate the effects for those living near sources of TRAP.
He suggested the key is to reduce the amount of air pollution entering your home and to lower levels of indoor air pollution.
  • Keep windows and doors closed during high-pollution periods (typically rush hours and hot, stagnant days)
  • Seal air leaks around windows, doors, and ducts
  • Run heating, ventilation, and air conditioning (HVAC) fans continuously, and change filters monthly
  • Invest in a high-efficiency particulate air (HEPA) purifier rated for your room size
  • Minimize indoor pollution sources such as candles, incense, and harsh cleaning products
Previous research from 2021 found that the effect of pollution on our sense of smell could be reversible if sources of PM2.5 components are better controlled.
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A Wake-Up Call

George Carrillo, the former director of social determinants of health for Oregon, recalled how the early pandemic offered a glimpse of cleaner air when traffic decreased dramatically.

“During the pandemic, many of us saw the air become clearer, skylines reappear, and waterways improve,” Carrillo said. “While it was an incredibly tragic time, it underscored the enormous benefits of reduced pollution. Clean, fresh air cannot just be a temporary outcome of a global crisis. We need it every day.” It’s important to note that the study could not establish that pollution directly caused loss of smell. However, researchers emphasized the study’s strengths, including the use of high-resolution pollution exposure estimates and a large, well-characterized population sample.

The researchers plan to expand their investigations by conducting nationwide analyses and longitudinal studies to better understand how long-term pollution exposure influences cognitive decline over time.

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