A new study published in the Journal of Allergy and Clinical Immunology reports that people exposed to polluted air out of doors show more severe symptoms of rhinitis, a very common condition also called a cold. This is due to an inflammation of the nasal mucosa.
Rhinitis affects 20% to 50% of the people of the world, and manifests as congestion, sneezing, rhinorrhea or nasal discharge, nasal irritation and sometimes a decreased sense of smell. Though it is such a common condition, few facts are at hand about what actually causes it to happen.
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Polluted air contains particles of various sizes, called airborne particles. These can be micrometers to millimetres in radius, and may be composed of liquids or solids, suspended in the air. The particles known to be of greatest harm are those under 2.5 micrometers in size, part of the family of fine particular matter (FPM) comprising particles less than 10 micrometers in size. These are distinguished as PM2.5 and PM10 respectively. PM 2.5 also reduce visibility and cause haziness at high concentrations.
The danger posed by PM 2.5 is chiefly due to the small size of the particles which allows them to penetrate deep into the respiratory tract, up to the level of the lungs. This not only causes lung irritation and exacerbates asthma as well as heart disease but can also produce irritation of the upper respiratory tract, producing the classic symptoms of a cold. When exposed to these over the long term, it is associated with chronic bronchitis, impaired lung function and higher rates of dying of lung cancer and heart disease.
Rhinitis is a condition that is linked with asthma, a state of hyper-reactivity of the airways where they constrict and become inflamed on exposure to apparently innocuous substances like pollen. However, asthma is known to be exacerbated in the presence of air pollution. This association motivated the current study on whether rhinitis is also linked to exposure to air pollution over the long term.
The researchers looked at 1400 patients with rhinitis from 17 different cities in various European countries. These range from Barcelona in Spain to Umea in Sweden. All the subjects were assessed by a questionnaire about the severity of their symptoms and how it interfered with daily activities. The level of air pollution in each of these cities was also derived from the European Study of Cohorts for Air Pollution Effects (ESCAPE).
The study found that the most severe rhinitis symptoms are found in people living in cities where the levels of PM10 and PM2.5 are highest. An increase in the PM2.5 level by 5 μg/m3 is linked to a 17% increase in the chances of severe rhinitis, especially with respect to symptoms like congestion of the nose, irritation and sneezing. On the other hand, the presence of NO2 at significant levels is found to cause an increase in nasal discharge and congestion of the mucosa.
Both PM and NO2 are mostly due to vehicular pollution. They are thought to produce different effects because of the difference in the way in which they act on the respiratory tract, even though both cause inflammation.
Says lead author Emilie Burte, “The role of these pollutants in the severity of symptoms is probably linked to oxidative stress, apoptosis (a process by which irreparably damaged cells are eliminated) and inflammation. Our findings suggest that the effect of airborne particulate matter differs from that of gaseous emissions (NO2), probably because their respective mechanisms of action provoke different inflammatory responses in the respiratory tract; however, more studies are needed to validate this hypothesis.”
The current study helps to clarify the role of airborne particles in rhinitis which is a very common even if not disabling disease. It is a major issue in public health, affecting the productivity and wellbeing of those suffering from it. As a result, it taxes public health resources out of proportion to its position as a non-fatal disease, due to the urgent need for treatment that most sufferers feel, the percentage of absenteeism it provokes and the general decline in productivity due to the misery it causes.
Long-term air pollution exposure is associated with increased severity of rhinitis in 2 European cohorts Burte, Emilie et al. Journal of Allergy and Clinical Immunology, https://www.jacionline.org/article/S0091-6749(19)31636-7/abstract