There are bacteria that choose to live in your nose, and that’s actually a good thing.

Belgian studies suggest that people with chronic nasal and sinus inflammation have fewer lactobacilli in their upper respiratory tract than healthy controls.

The researchers also were able to identify a specific strain of the bacteria that has evolved to better survive the nose’s unsurprisingly oxygen-rich environment, allowing them to trial a nasal spray that could deliver lactobacilli where they are needed.

Lactobacilli are friendly rod-shaped bacteria that have pathogen-inhibiting properties because they produce lactic acid through sugar fermentation. They are commonly found doing good in the gut, urinary system and genital tracts.

To see whether they play a similar role in the upper respiratory tract, a team led by Sarah Lebeer from the University of Antwerp compared nose bacteria from 100 healthy individuals and 225 chronic rhinosinusitis patients.

They looked at the prevalence of 30 different families of bacteria in the upper respiratory tract and found that the healthy people had a greater abundance of lactobacilli – up to 10 times more in some parts of the nose.

A closer look revealed bacteria strains that not only have unique genes to cope with the higher oxidative stress levels in the nose, but also flexible, hair-like tubes called fimbriae, which allow them to adhere to the surface cells in the nose.

Traditional follow up trials with mice weren’t possible because mice have very different noses and don’t tend to get the same allergies and inflammations. However, lactobacilli’s safe history allowed Lebeer and colleagues to work directly with humans.

Their initial aim was to test whether bacteria introduced via a spray could survive and thrive in the nose (which has a pretty good filter for dealing with foreign substances) but anecdotal evidence from some participants also suggested that fewer nasal problems were the result.

The next stage is to understand whether the fimbriae and the ability to endure oxidative stress are key to beneficial anti-inflammatory properties of the strain, as well as to identify which antimicrobial molecules the strain produces in addition to lactic acid.

“We think that certain patients would benefit from remodelling their microbiome and introducing beneficial bacteria in their nose to reduce certain symptoms,” says Lebeer. “But we still have a long way to go with clinical and further mechanistic studies.”

The study is described in a paper in the journal Cell Reports.