Does the use of antimicrobial mouthwash or nasal spray by people who are not actively suspected of having COVID-19 - or by their healthcare workers - protect their healthcare workers when they undertake 'aerosol-generating procedures' on them?

Why is this question important?

COVID‐19 is an infectious disease caused by the SARS‐CoV‐2 virus. Most people infected with COVID-19 develop a mild to moderate respiratory illness, and some may have no symptoms (asymptomatic infection). Others experience severe symptoms and need specialist treatment and intensive care.

COVID-19 spreads from person to person primarily through droplets that are produced when an infected person coughs, sneezes or talks. A person can also become infected by touching a surface or object that has viral droplets on it, and then touching their own mouth or nose.

Some people with COVID-19 do not have any symptoms, therefore they might not be known to be or suspected of being infected. However, they might still be able to pass the infection on to others. This means that healthcare workers who are treating them may be at risk of catching the infection. Risk of infection may be particularly high when healthcare workers undertake 'aerosol-generating procedures', which are medical procedures that cause the patient to produce many small droplets. For example, people who have surgery under general anaesthesia, or people with a lung disease that makes breathing difficult (such as pneumonia), may need to be placed on a ventilator (artificial breathing machine) to help them breathe. This requires a healthcare worker to insert a tube through the patient's mouth, into their airway – a procedure during which many small droplets are likely to be produced by the patient. Similar droplets can be produced during routine dental procedures, such as drilling or scaling of teeth.

Patient or healthcare worker use of antimicrobial mouthwash (to rinse the mouth) or nasal spray (sprayed into the nose) might help to protect healthcare workers against infection by COVID-19. Antimicrobial mouthwash and nasal spray are liquids that kill or stop the growth of micro-organisms such as viruses or bacteria.

As with any medical treatment, antimicrobial mouthwash and nasal spray have potential risks as well as benefits. It is possible that using mouthwash or nasal spray could cause a variety of unwanted (adverse) effects, including irritation, allergic reactions or loss of smell. It may also remove micro-organisms from the mouth or nose that are useful for protecting the body against infection.

We set out to assess the benefits and risks of self-administration of antimicrobial mouthwashes and nasal sprays by patients without a known or suspected COVID-19 infection, or the healthcare workers who treat them with aerosol-generating procedures, by reviewing the research evidence.

How did we search for evidence?

Our team of researchers searched the medical literature for studies that compared the effects of patients or healthcare workers self-administering any antimicrobial mouthwash or nasal spray against using no treatment, water or a salt solution.

What did we find?

We found no completed, or ongoing, studies to include in this review.

What does this mean?

There is currently no evidence relating to the benefits and risks of healthcare workers' or patients' use of antimicrobial mouthwashes or nasal sprays to protect healthcare workers who undertake aerosol-generating procedures on patients without a known or suspected COVID-19 infection.

We need studies to be conducted so that we can answer this important clinical question.

How-up-to date is this review?

We last searched for evidence on 1 June 2020. This review covered research that was available up to that date, but did not consider any evidence that may have been produced since then.

Authors' conclusions: 

We identified no studies for inclusion in this review, nor any ongoing studies. The absence of completed studies is not surprising given the relatively recent emergence of COVID-19 infection. However, we are disappointed that this important clinical question is not being addressed by ongoing studies.

Read the full abstract...

COVID-19 infection poses a serious risk to patients and – due to its contagious nature – to those healthcare workers (HCWs) treating them. The risks of transmission of infection are greater when a patient is undergoing an aerosol-generating procedure (AGP). Not all those with COVID-19 infection are symptomatic, or suspected of harbouring the infection. If a patient who is not known to have or suspected of having COVID-19 infection is to undergo an AGP, it would nonetheless be sensible to minimise the risk to those HCWs treating them.

If the mouth and nose of an individual undergoing an AGP are irrigated with antimicrobial solutions, this may be a simple and safe method of reducing the risk of any covert infection being passed to HCWs through droplet transmission or direct contact. Alternatively, the use of antimicrobial solutions by the HCW may decrease the chance of them acquiring COVID-19 infection. However, the use of such antimicrobial solutions may be associated with harms related to the toxicity of the solutions themselves or alterations in the natural microbial flora of the mouth or nose.


To assess the benefits and harms of antimicrobial mouthwashes and nasal sprays administered to HCWs and/or patients when undertaking AGPs on patients without suspected or confirmed COVID-19 infection.

Search strategy: 

Information Specialists from Cochrane ENT and Cochrane Oral Health searched the Central Register of Controlled Trials (CENTRAL 2020, Issue 6); Ovid MEDLINE; Ovid Embase and additional sources for published and unpublished trials. The date of the search was 1 June 2020. 

Selection criteria: 

This is a question that urgently requires evidence, however at the present time we did not anticipate finding many completed RCTs. We therefore planned to include the following types of studies: randomised controlled trials (RCTs); quasi-RCTs; non-randomised controlled trials; prospective cohort studies; retrospective cohort studies; cross-sectional studies; controlled before-and-after studies. We set no minimum duration for the studies.  

We sought studies comparing any antimicrobial mouthwash and/or nasal spray (alone or in combination) at any concentration, delivered to the patient or HCW before and/or after an AGP.

Data collection and analysis: 

We used standard Cochrane methodological procedures. Our primary outcomes were: 1) incidence of symptomatic or test-positive COVID-19 infection in HCWs or patients; 2) significant adverse event: anosmia (or disturbance in sense of smell). Our secondary outcomes were: 3) COVID-19 viral content of aerosol (when present); 4) change in COVID-19 viral load at site(s) of irrigation; 5) other adverse events: changes in microbiome in oral cavity, nasal cavity, oro- or nasopharynx; 6) other adverse events: allergy, irritation/burning of nasal, oral or oropharyngeal mucosa (e.g. erosions, ulcers, bleeding), long-term staining of mucous membranes or teeth, accidental ingestion. We planned to use GRADE to assess the certainty of the evidence for each outcome.

Main results: 

We found no completed studies to include in this review.  

Health topics: