[chris (OP)]

Aaron has been in touch to say

Dear Chris,

I am a regular listener of the Naked Scientists. I have listened to all of your shows from the beginning. I know that Chris has a pet hate for the wearing of surgical masks as a preventative measure during this awful viral outbreak. I am living in China.

There is one major benefit of wearing these masks that I feel Chris may have overlooked. The masks stop an individual from touching their mouth or nose. As Chris has mentioned many times in various podcasts the most important thing a person can do is wash their hands regularly..So a physical barrier acting as a constant reminder to avoid touching your face must be a positive thing. I feel to state that the masks do nothing to prevent catching the virus is therefore not entirely true.

As a doctor I think Chris has a valid point in citing various studies that indicate wearing surgical masks has little or no effect on flu prevention. I would be interested to hear his opinion on the masks acting as a psychological reminder to avoid touching ones face.

Thank you all for your wonderful podcasts.

What does everyone think?

[chris (OP)]

Thank you for your kind feedback and for passing on your thoughts.

You are quite right: these masks do have a psychological effect in terms of reminding people about infection risks, but I'm not sure there's any evidence that people wearing these things touch their faces - or the masks - any less frequently.

In fact, by definition, mask wearers need to touch their faces more frequently: to put on and take off the mask - for instance to eat and drink; o blow their noses; adjust the mask etc. This matters, because contact between the mask and potentially contaminated fingers can apply viruses to the mask surface; the particles can then make their way through the mask and be inhaled.

I would advise that, for medical staff and certain patients, wearing masks is highly effective at defending against disease spread, so long as they are used correctly.

But for the average - uninfected - person, using low-grade or non-medical standard masks, there is no benefit whatsoever and risk might increase for the reason outlined above. I would therefore forego using them.

[Petrochemicals]

Thank you for your kind feedback and for passing on your thoughts.

Is that sarcasm Dr Chris ? Anyhoo I save to suggest your approximation of masks is wayward

My own theory is that facemasks are brilliant for anyone who is sneezing coughing or dribbling in anyway, to help not spread the virus. As for protection against catching viruses and pollution they are not very effective exept for incidental passing threats direct to the face. There is a reason that modern respirator equipment is deemed ineffective unless "face fit". Stopping airborn water droplets is more desirable !

https://www.hse.gov.uk/respiratory-protective-equipment/fit-testing-basics.htm

[Colin2B]

Thank you for your kind feedback and for passing on your thoughts.

Is that sarcasm Dr Chris ?

I don’t think so. My experience is that Chris welcomes any opinion within the rules, feedback is always useful.

To add my opinion (and this is opinion, not based on knowledge) surgical masks are there to prevent infections from doctor to patient. Although they might stop some airborne droplets they also raise the humidity a person is breathing which could change the survival rate of any virus. I think the points Chris makes about contamination of the mask is valid.

[Petrochemicals]

Thank you for your kind feedback and for passing on your thoughts.

Is that sarcasm Dr Chris ?

I don’t think so. My experience is that Chris welcomes any opinion within the rules, feedback is always useful.

To add my opinion (and this is opinion, not based on knowledge) surgical masks are there to prevent infections from doctor to patient. Although they might stop some airborne droplets they also raise the humidity a person is breathing which could change the survival rate of any virus. I think the points Chris makes about contamination of the mask is valid.

It does make a wonderful evapouration medium, this will surely take water droplets with it. Given that C19 survives for 3 days in outdoor conditions(so I have been informed), this makes a wonderful contamination device. Perhaps mask disposal after 15 minutes for those who are forced to wear them ?

I do not think the humidity the person is breathing will alter, if you have ever used a propper sealed respitator from the atmosphere, not gas tank, you will notice the difference in effort to draw breath.  Face masks with the elastic draw of breath  just goes up the sides !

[Bored chemist]

It does make a wonderful evapouration medium, this will surely take water droplets with it.

You might be "sure" of that, I'm not.
I know that water evaporates, but leaves things like salt behind.

Perhaps mask disposal after 15 minutes for those who are forced to wear them ?

What orifice did you get that number from?

Having said that there's some truth to this

  Face masks with the elastic draw of breath  just goes up the sides !

Unless the mask fits properly (and there's a fairly involved testing method to see if it does) then all it does is stop you picking your nose.

[id2000]

I struggle trying to make sense of the conflicting information about face masks. The Guardian mentions that some studies indicate masks can reduce the risk of infection by a factor of 5.

I have noticed that if I spend time talking to a friend who is coughing or spluttering then it is not unusual to notice tiny droplets on my spectacles when I remove them. Presumably these are the droplets that can carry infectious material? In which case, if spectacles form an effective barrier for the eyes, why not face masks for the nose & mouth?

I appreciate that walking in the street I am unlikely to encounter the virus so there is no point wearing one, but what about on a flight or long distance bus journey where one could be a few seats away from an infected person?

I am due to make two coach trips; one in and one out of Oxford (which seems to be a bit of a hot spot for Corona). I am in an at-risk group and so wonder if I should wear a mask on the coach or perhaps it would be better to cancel the trip.

[Bored chemist]

In which case, if spectacles form an effective barrier for the eyes, why not face masks for the nose & mouth?

Spectacles don't have holes in them to let air through.
Also the tiny droplets can be swept round masks or glasses by air currents- notably those due to breathing.

If the mask isn't properly fitted and sealed it's really not much use.

There's a pessimistic estimate that there are about 10,000 undiagnosed cases in the UK at the moment.
And we have a population of about 70 million.
So there's a roughly 1 in 7000 chance of any particular person having it.
Are there 7000 people on the coach?
If not, it's likely that nobody on that coach has the virus.

Can we please leave the masks for those who actually need them?

[id2000]

Spectacles don't have holes in them to let air through.

I had assumed that a droplet that is visible to the naked eye would not penetrate say an FFP2 mask?

Also the tiny droplets can be swept round masks or glasses by air currents- notably those due to breathing.

But presumably the exposure would be reduced?

There's a pessimistic estimate that there are about 10,000 undiagnosed cases in the UK at the moment.
And we have a population of about 70 million.
So there's a roughly 1 in 7000 chance of any particular person having it.
Are there 7000 people on the coach?
If not, it's likely that nobody on that coach has the virus.

Yes, this was my original thinking - the risks seem vanishingly small - but after thinking about it some more I am less sure.

Firstly, I am travelling through Oxfordshire so I could use the Oxfordshire stats (not all the passengers will originate from Oxfordshire but I am erring on the side of caution). Up to 12th March there were 22 cases recorded in Oxfordshire - when I travel I assume there will be 44 recorded cases (assuming cases double every 4 days).

When the 10,0000 figure for the UK was estimated it was approximately 15 times the recorded number at that time. So applying the same rule to the Oxfordshire number gives 15x 44 = 660 actual cases when I travel.

The Oxfordshire population is 687,524 so 660/687,524 = 0.00096. So that I think is the chances of someone in the local population being infected. Unfortunately I have to change buses in Oxford - so two buses on the outward trip and two on the return - say 30 passengers in each = 120 in total. So I think the probability of a passenger being free from infection is 1 - 0.00096 =  0.99904 and the probability of all 120 being free of it = 0.99904^120 = 0.89 - so actually an 11% risk of encountering an infected person- no longer vanishingly small. I am not sure if I have calculated the probabilities correctly - 40 years since I did them in the classroom.

Can we please leave the masks for those who actually need them?

I have a half used pack of 3M FP2 masks acquired long before Corona for DIY work so would not be depriving others.

[Bored chemist]

I had assumed that a droplet that is visible to the naked eye would not penetrate say an FFP2 mask?

True, but the droplets that are small enough to get inhaled may be small enough to get through (or round).
A droplet doesn't need to be visible to be infectious.

[Bored chemist]

This may help
https://www.hse.gov.uk/research/rrpdf/rr619.pdf

[Colin2B]

I do not think the humidity the person is breathing will alter, if you have ever used a propper sealed respitator from the atmosphere, not gas tank, you will notice the difference in effort to draw breath.  Face masks with the elastic draw of breath  just goes up the sides !

Whenever I’ve used them in cold air I’ve noticed condensation on the outlets and sometimes on inside.
I decided to try testing humidity yesterday. I used a 3M disposable dust mask P2. Relative humidity was 48%, after 2min I put the probe inside the mask and recorded 95%. Not surprising as we breath out a lot of moisture.

This may help
https://www.hse.gov.uk/research/rrpdf/rr619.pdf

Also, this one might, backs up much of what you are saying:

 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5058571/

[Petrochemicals]

I do not think the humidity the person is breathing will alter, if you have ever used a propper sealed respitator from the atmosphere, not gas tank, you will notice the difference in effort to draw breath.  Face masks with the elastic draw of breath  just goes up the sides !

Whenever I’ve used them in cold air I’ve noticed condensation on the outlets and sometimes on inside.
I decided to try testing humidity yesterday. I used a 3M disposable dust mask P2. Relative humidity was 48%, after 2min I put the probe inside the mask and recorded 95%. Not surprising as we breath out a lot of moisture.

Did your earlier comment mean the humidity of the mask and the breeding ground for bacteria on the wearers intake of breath, rather than infecting anyone else, so possibly infecting the wearer? I was thinking more about leaks.

[Colin2B]

Did your earlier comment mean the humidity of the mask and the breeding ground for bacteria on the wearers intake of breath, rather than infecting anyone else, so possibly infecting the wearer?

Context was supporting @chris in his comment about contamination, when fitting, adding to infection of wearer. Extra humidity can increase risk of viruses in droplet or infected material surviving.

[set fair]

Taking what the government and health authories say as true ie masks won't offer any protection to the wearer but they will reduce infections passed on by the wearer.

Consider the first 100 people to be infected in the UK and let us say they went on to infect 250 more people. Then the question is :- would tthey have infected less than 250 people had all 100 of them been wearing face masks from the moment of their being infected? I don't think the answer can be anything but yes. Conclusion, everbody should be wearing masks.

[Petrochemicals]

I know that someone was ridiculed by the wider stage for suggesting medical staff could use military cbn respiration devices, but given that medical staff are dying at 12 percent of covid dead, surely its a good idea, as face masks OBVIOUSLY DO NOT WORK.

[set fair]

I know that someone was ridiculed by the wider stage for suggesting medical staff could use military cbn respiration devices, but given that medical staff are dying at 12 percent of covid dead, surely its a good idea, as face masks OBVIOUSLY DO NOT WORK.

Clearly the masks don't prevent medical staff from being infected, but that doesn't mean that they don't reduce the spread. The medical staff wash their hands and still get infected that doesn't mean that OBVIOUSLY HAND WASHING DOES NOT WORK. For a look at the difference between counties using masks and those not, see the chart at 19:20 in this video

We should all be wearing masks, even home made cotton ones washed and reworn slow the rate of spread. I wouldn't argue with your comment on military cbn respiration devices.

[Petrochemicals]

You have to ask of our motives really, during Ebola, we thought they where adequate

http://animalnewyork.com/2014/picture-ebola-inside-west-african-isolation-ward/

[Petrochemicals]

I know that someone was ridiculed by the wider stage for suggesting medical staff could use military cbn respiration devices, but given that medical staff are dying at 12 percent of covid dead, surely its a good idea, as face masks OBVIOUSLY DO NOT WORK.

Clearly the masks don't prevent medical staff from being infected, but that doesn't mean that they don't reduce the spread. The medical staff wash their hands and still get infected that doesn't mean that OBVIOUSLY HAND WASHING DOES NOT WORK. For a look at the difference between counties using masks and those not, see the chart at 19:20 in this video .

yep surgical masks prevent infection to some degree but dont protect the surgeon. As for the medical staff, what precautions are they not taking that they could other than better facial protection. There is a hole in the system, what is it? You can be sure that all hospital patients are treated inline with the standards of korean public apparel, and then some, so even surgical masks worn by patients are not very effective.

I doubt very much that medical staff are doing the wearing vinyl gloves and then having a fag with them on that I have seen. Or the licking of things in the way children have a tendancy too.

[alancalverd]

The primary purpose of ordinary surgical kit is to prevent reasonably fit staff infecting the patient with common bugs like streptococcus. The positive pressure incoming air to theaters and critical wards is highly filtered and thus fit to breathe. But where the patient is known to carry a highly infective and novel virus, the problem is inverted and you need to step up the protection substantially, hence the full body, helmet and respirator kit worn by ebola nurses and now required for COVID.

As far as the general public is concerned, the probability and intensity of exposure are lower and can be further reduced (but not eliminated) in both directions with a simple mask.