Why you have a runny nose, even when you aren't sick

Portrait of ill business woman at work (iStock)

Do you find yourself sniffing and reaching for tissues all year round even when it isn’t allergy season and you don’t have a cold?

You may want to take a look at the air around you, quite literally.

Air pollution has been linked to inflammation in the nasal and sinus tissues in a new study.

The inflammation can leave you with a runny nose all year round, scientists discovered.

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In tests on mice researchers from John Hopkins University School of Medicine in the US found air pollutants damaged the upper respiratory system.

It has long been known that these pollutants and smog raise rates of respiratory problems like asthma but this is the first time it has been linked to the sniffles.

Dr Murray Ramanathan, lead author of the study, said: “In the US, regulations have kept a lot of air pollution in check, but in places like New Delhi, Cairo or Beijing, where people heat their houses with wood-burning stoves, and factories release pollutants into the air, our study suggests people are at higher risk of developing chronic sinus problem.”

To test their theory they exposed 38 eight-week-old mice to either filtered or unfiltered air from the city of Baltimore five days a week for 16 weeks.

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The mice that were exposed to pollution presented with a higher white blood cell count after that time, indicating they were suffering from higher levels of inflammation.

They also had higher levels of messenger RNA – the blueprints of DNA needed to make proteins – in the genes associated with inflammation.

Dr Ramanathan added: “Inflammation that attracts eosinophils [a type of white blood cell] is what happens in the lungs of people with asthma, so essentially the chronic exposure to air pollution in mice is leading to a kind of asthma of the nose.”

Further tests showed the surface layer inside the nose of the mice who had breathed in the pollution was 30 to 40 per cent thicker than those who hadn’t.

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They also found much higher levels of the protein serum albumin in the mice that breathed in the polluted air, which indicates the pollutants had broken through the barrier in the nasal passage and sinuses.

Dr Ramanathan said: “We’ve identified a lot of evidence that breathing in dirty air directly causes a breakdown in the integrity of the sinus and nasal air passages in mice.

“Keeping this barrier intact is essential for protecting the cells in the tissues from irritation or infection from other sources, including pollen or germs.”

First published on The Sun.