Can a Healthy Nose Help Protect You From COVID?

Analysis by Dr. Joseph Mercola Fact Checked

nasal microbiota

Story at-a-glance

  • Lactobacilli are an important part of a balanced gut microbiome; several are also present in the nasal cavity, having adapted to the environment
  • Lactobacillus usually prefers an oxygen-poor environment, but L. casei have adapted to living in the nose, with hair-like tubes that help adhere the bacteria to the epithelium
  • The bacteria inhibit the growth of pathogens. A proof-of-concept nasal probiotic spray tested well in human trials
  • Although a healthy nasal microbiome can help deter infection, there are current strategies to support your immune health, such as optimizing your vitamin D level and using quercetin and zinc


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

You may have considered the microbiome of your gut an important part of your immune system, but have you thought about the bacteria living in your nose as friend or foe? In recent years, with advances in laboratory technology and testing, the important role of microbiota in support of your immune system is becoming clearer.

The recent pandemic, with the ongoing debate over the efficacy of using masks to cover your nose and mouth, may be driving rising interest in the bacterial reservoir of your nose. Many types of viral or bacterial infections can enter through the nose, such as the common cold, flu, SARS-CoV-2 and acute bacterial rhinosinusitis, which often starts as a viral infection.1

Viruses that enter the body through the nose can trigger an upper respiratory infection and may bring about a runny nose, fever, chills and coughing. As the mucosa becomes inflamed, it creates an environment where bacteria can thrive.

Research has shown that the microbiota in your nose change as you age and have an immunomodulatory effect.2 This implies there may be a role for probiotic supplementation to help support your nasal microbiota and therefore bolster your immune response to airborne pathogens.

Chronic Sinusitis Has Significant Impact on Daily Living

The reported incidence of chronic rhinosinusitis fluctuates from 1%3 of the population to 11.5%, depending upon the severity of symptoms being measured.4 In one sample of 10,336 U.S. adults, data were collected using a questionnaire to determine symptoms of chronic rhinosinusitis, the impact of the symptoms on the individual's life, how long they lasted and the treatment used.

The researchers found that 11.5% of those who responded reported symptoms and duration that met the criteria for chronic rhinosinusitis. Interestingly, about 10% of those with the condition also reported having a diagnosis of nasal polyps.

An acute infection will last less than four weeks, but chronic sinusitis will last at least 12 weeks with several episodes of acute infection before moving into the chronic stage. Typical symptoms include:5,6

Thick yellow to green nasal discharge and postnasal drip

Pain, tenderness and swelling around facial structures such as the eyes, nose and forehead

Pain in the face that gets worse when you lean forward

Pain in the upper jaw or teeth

Reduced sense of smell and taste

Cough or throat clearing

Ear pressure


Bad breath


Although the symptoms are similar, there are different types of sinusitis including acute, chronic and recurrent.7 Acute sinusitis lasts up to four weeks and can go away with little, if any, treatment. Recurrent sinusitis can happen four or more times in one year with periods of time without symptoms. With chronic sinusitis the symptoms are there almost all the time.

The mother of Sarah Lebeer, a microbiologist and microbiome researcher, suffered from chronic sinusitis. Lebeer is from the University of Antwerp and became interested after her mother had surgery to treat headaches and chronic rhinosinusitis. She commented on the inspiration for the team's current study:8

"My mother had tried many different treatments, but none worked. I was thinking it's a pity that I could not advise her some good bacteria or probiotics for the nose. No one had ever really studied it."

Nasal Bacteria in Healthy People Are Different

Before this study, Lebeer had been studying the use of probiotics for the gut and vagina to improve health. However, her focus changed as she contemplated the potential use for probiotics to help treat chronic rhinosinusitis.

The study began by comparing the bacteria found in 100 healthy people to 225 people with chronic rhinosinusitis.9 They chose 30 different families of bacteria and discovered the healthy group of individuals had up to 10 times more lactobacilli in some parts of the nose than did those with chronic rhinosinusitis.

Lactobacilli are an important part of a balanced gut microbiome. You may have heard this class of bacteria advertised as the beneficial bacteria in yogurt, lactobacillus acidophilus.10 The group found the most abundant lactobacilli in the healthy group of individuals belonged to the Lactobacillus casei group, which had been given a new genus name: Lacticaseibacillus.11

Following the discovery, the team sought to cultivate the species. After isolation and genome sequencing, they found the bacteria appeared to be similar to available probiotics for oral consumption found in food. However, there were indications that they were distinctive and had developed adaptations to the upper respiratory tract.

Most lactobacilli prefer the relatively low oxygen environment in the gut, but this genus appeared to have adapted to higher oxygen levels, oxidative stress and high airflow in the nasal cavity.12 Another adaptation the team found was the ability of the bacteria to adhere to the nasal epithelium and therefore prevent the body from clearing it.13

The bacteria had "flexible, hair-like tubes called fimbriae, which allow them to adhere to the surface cells in the nose, indicating an interaction between the bacteria and host."14

In their analysis they found Lactobacillus casei inhibited the growth of pathogens found in the nasal cavity and the respiratory epithelium tolerated the bacteria as they produced fewer interleukin and tumor necrosis factors in comparison to the pathogens.15

Probiotic Nasal Spray Is Proof of Concept

The next step for the team was to evaluate their findings in vivo, meaning, outside the lab in an actual plant or animal. As described in Cell Reports, animal studies are usually the step in between lab-based testing and human trials. However, in this case, using an animal model would have been difficult since most have different upper respiratory anatomy, physiology and pathogens than humans.16

The team applied for and was granted approval for human testing based on the history and safety of lactobacillus in the nose of healthy and ill individuals. They engaged 20 healthy volunteers who used the nasal probiotic twice a day for two weeks.

The primary outcome measurement in this part of the study was the fitness of the bacteria in the nasopharynx of the participants and to demonstrate the potential of a probiotic supplement administered through the nose. Nasal samples were taken at five minutes, 10 to 16 hours and two weeks after administration of the spray.

The researchers demonstrated temporary colonization in many and it could still be detected in two of the participants after two weeks.17 Lebeer was encouraged by the results, which they called a "proof-of-concept nasal spray," saying:18

"Sinusitis patients don't have a lot of treatment options. We think that certain patients would benefit from remodeling their microbiome and introducing beneficial bacteria in their nose to reduce certain symptoms. But we still have a long way to go with clinical and further mechanistic studies."

Healthy Nasal Microbiome May Offer Infection Protection

Bacterial diversity in individuals with chronic rhinosinusitis has been analyzed as scientists have searched for treatment options. In one study, researchers compared the sinus microbiota in six healthy participants and nine patients with chronic rhinosinusitis.19

They found bacterial variation was explained by personal differences rather than disease: Some were smokers; others had Staphylococcus and/or a variety of microbiota, compared to relatively few types in the healthy individuals.

In another paper, scientists hypothesized there was an association between the dysbiosis found in the nasal cavities of people with chronic rhinosinusitis and alterations in their immune system.20

In a third study, researchers looked at the microbial colonization of the upper respiratory tract as it related to an individual's age, lifestyle, diseases and immune responses.21 They found that the microbiome of adults is different from that of children. Children have a denser and higher bacterial load that is less diverse than that of adults.

Alterations in the nasal microbiome begin to change in middle age with bacteria often being found in the oropharyngeal area. This may have an impact on the increased risk of COVID-19 for older individuals. In their review of studies, they found that cigarette smoking changes the airway microbiome, raising the number of potential pathogens and reducing the robust composition of beneficial bacteria over time.

Additionally, there may be a link with nasal microbiome and neurological diseases, such as Parkinson's disease, Alzheimer's disease and multiple sclerosis.

Medications and other therapies administered inside the nose may alter the microbial activity in your upper respiratory tract. These can include corticosteroids, rinses, antibiotics and antihistamines. The study team said that nasal rinses using isotonic saline or hypertonic saline can rid the nasal mucosa of inflammatory compounds and pollutants.

However, tap or well water are of concern because they can contain bacteria or parasites. The authors reported that distilled water is what's currently recommended. The study was published six months before Lebeer's study, and the team also suggested:22

"The next logical step would be the application of probiotics nasally, although a potential risk of inflammation in the lower airways due to aspiration into the lung might exist."

More Steps to Reduce Severe Disease From COVID-19

While it appears that administering probiotics intranasally may be an option in the future, it's important to take action on the strategies you can use today to reduce your risk of infectious disease, including COVID-19. As I've written, I believe one of the simplest and easiest ways preventing severe disease is to optimize vitamin D.

Unfortunately, many people across the world are vitamin D deficient, which can have a significant impact on your risk of testing positive for COVID-19, severe infection and death from it. To improve your immune function and lower your risk, you'll want to raise your vitamin D to a level between 60 ng/mL and 80 ng/mL.

For a quick summary of the key steps to raise your vitamin D level and a short discussion of the data, see "Vitamin D in the Prevention of COVID-19." As important as vitamin D is to your immune and overall health, there are other strategies you may consider that lower your risk of severe disease.

In "How to Fix the COVID-19 Crisis in 30 Days," I discuss some of these using recent scientific evidence and experts. Dietary strategies, quercetin and zinc supplementation and the MATH protocol are just some of the information you'll find.

I encourage you to share this with your friends and relatives. By working together to share health information the media is not willing to publicize, you can make a real difference in the number of people who may stay healthy and enjoy their best life.


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