Why are we gradually losing our sense of smell?

The sense of smell is key in our social interactions

Our sense of smell is one of the largest windows we have to experience the richness of the world around us. It plays a vital role in everything we taste, in our social interactions, and can even help us detect potential threats.

But an invisible hazard in the air we breathe could be eroding our olfactory powers. Many people were able to experience what it is like to lose their sense of smell when infected with covid-19.

Loss of smell is known as anosmia and can have a substantial effect on our general well-being and quality of life. But while the loss of this important sense due to a sudden respiratory infection is often temporary, there may be another factor that has been gradually eroding our sense of smell for years: air pollution.

pollution and smell

Exposure to PM2.5 – a collective name used to describe the small particles of air pollution emitted by combustion from cars, power stations and our homes – has previously been linked to the development of “olfactory dysfunction,” but typically only in occupational or industrial settings.

Now a new study is beginning to show the true scale of the pollution we breathe, and the damage it can cause. And the results are up to all of us.

Below our brain – just above our nasal cavities – is the olfactory bulb. This sensitive piece of tissue is packed with nerve endings and is essential to the incredibly varied olfactory image we get from our noses.

It is also our first line of defense against viruses and contaminants that could enter the brain. However, with repeated exposure to external agents, these defenses slowly wear down or break down.

discovering the culprit

Until recently, the scant scientific research on this topic included a 2006 Mexican study that used strong odors (of coffee and orange) to show that Mexico City residents – who constantly battle air pollution air- tended to have on average a poorer sense of smell than people living in rural areas of the country.

With the help of colleagues—including environmental epidemiologist Zhenyu Zhang, who mapped historical data on air pollution in the Baltimore area—Ramanathan was able to develop a case-control study of data with a group of 2,690 patients who they had attended Johns Hopkins Hospital for a period of four years.

About 20% had anosmia and most did not smoke, a habit known to impair the sense of smell. Sure enough, PM2.5 levels were found to be “significantly higher” in the neighborhoods where the anosmia patients lived compared to healthy control participants.

Even when adjusting for age, gender, race or ethnicity, body mass index, alcohol use, or tobacco use, the findings were the same: “Even small increases in ambient PM2.5 exposures may be associated with anosmia.”

Even more striking is that none of the Johns Hopkins patients lived in areas with excessively high air pollution: many lived in leafy areas of Maryland, and none came from pollution hotspots.

This suggests that even low levels of air pollution could cause problems over a long enough period.