Viruses and surgical masks

October 19, 2009 8:40 AM

Do the surgical masks that I see everyone wearing protect against viruses?

So, I've seen and hear of people wearing surgical masks or some variant of them when traveling, in order to guard against various strains of the flu.

Can these masks really protect against airborne viruses? My understanding is viruses are much smaller than bacteria or fungal spores. Do surgical masks adequately filter out viruses?

posted by dfriedman to health & fitness (15 answers total)

If it actually a surgical mask, and not one of those cheap dust masks you can buy at Home Depot, then the CDC thinks yes.

I have read, and it makes sense, that it's more effective for infected people to wear surgical masks if the virus is spread through sneezing and coughing. The droplet size decreases as it travels away from the infected person's mouth/nose, making a surgical mask less and less effective.
posted by muddgirl at 8:45 AM on October 19, 2009 [1 favorite]

Here in Ontario, the health authority says no. Reason being that most people use them improperly due to discomfort, and end up contaminating them with their hands anyway.
posted by sunshinesky at 8:46 AM on October 19, 2009

I think the viruses people get nervous about (flu) are transferred via the hands to the mouth and nose. I guess a mask might prevent accidental contact with those areas, but overall my understanding is it's not going to help much. The UK's Health Protection Agency agrees, more or less.
posted by BrokenEnglish at 8:47 AM on October 19, 2009

Article on this, which makes a distinction between surgical masks and N95 masks:

Results showed that surgical masks are not effective against illness or infection, MacIntyre says. ... N95 masks, on the other hand, were 56% effective against lab-confirmed respiratory viral infections and 75% protective against confirmed influenza.

I don't know that the N95 masks are comfortable enough to wear long term when traveling though. They are pretty tight.
posted by smackfu at 8:48 AM on October 19, 2009

Apparently, they are as effective as N95 respirators. However, the CDC isn't sure if N95 respirators are even effective, other than to keep people away from you, and to prevent you from touching your mouth and nose.
posted by cabingirl at 8:49 AM on October 19, 2009

They are more effective at preventing the mask wearer from spreading the virus than the other way around.
posted by caddis at 8:53 AM on October 19, 2009 [1 favorite]

A surgical mask would also prevent an infected person from sneezing/coughing into their hands and spreading the virus by touch. Not everyone has learned the vampire sneeze yet, as I have seen lots of people still sneezing into their open palms.
posted by muddgirl at 8:55 AM on October 19, 2009 [3 favorites]

The other thing a mask does is that it encourages people to stay away from you because they assume you'll get them sick. Try wearing one in a crowded mall during the December holiday season. People avoid you and really make you feel sub-human with their dirty looks, even if you're wearing it for your own protection and aren't sick. It's quite humiliating. However, it causes less personal contact with others, which can help prevent disease.
This is not just anecdotal personal evidence, there was also an article in the New York Times about this phenomenon a few months ago.
posted by k8lin at 9:21 AM on October 19, 2009 [1 favorite]

Regardless of what they tell you on TV, wearing an n95 respirator will help you avoid getting influenza. Oh, it may not be all that effective under the kind of rigid laboratory testing they are put through but you don't really care about that. It's not like you're planning to use the thing while working on a genetically engineered superbug with death the result if you catch it. In other words, it doesn't have to be all that effective to be useful to you.

Influenza is spread three ways. One, somebody sneezes or coughs the stuff into the air and you inhale it. Two, somebody sneezes or coughs the stuff onto their hands and then touches you, or you touch them, and then you touch your eyes, nose, or (to a somewhat lesser extent) mouth. Third, somebody sneezes the gunk onto a surface (doorknob, keyboard, money), you touch the surfance, and then you touch your eyes, nose, or mouth.

It's not clear whether n95 will stop the smallest airborne droplets. But that hardly means wearing a mask won't help. It may stop the droplets or at least provide some protection. If it does, great. But even if it doesn't it will interrupt the other modes of transmission to a pretty high degree. You can't touch your nose or mouth while you're wearing one, and it should be a constant reminder not to touch your eyes. If you are in the habit of thoroughly washing your hands before removing your mask (and possibly again after) that's a big impediment to the disease vector.

Most people don't wear the masks properly, of course. An n95 respirator is hot, uncomfortable, and just generally unpleasant to wear for any length of time. So people wear it but keep it way too loose. Or they are constantly adjusting it which, surprise, brings their hands very close to their eyes, nose, and mouth. And so on. But if you wear it properly it will help prevent transmission.

If you listen carefully they usually don't say on the news that wearing one is useless. They just say things like "we don't recommend it at this time" or "washing your hands is the best way to prevent transmission". That's because they don't want to give you bad information, but at the same time nobody is going to get on television and announce that wearing an n95 respirator while walking the streets is a good thing. It's just not the done thing.

I have a whole bunch of n95 respirators in a closet somewhere. I don't expect I'll be breaking them out any time soon.
posted by Justinian at 9:45 AM on October 19, 2009 [2 favorites]

Most surgical masks are made, well, for surgeons. The goal is to prevent them from breathing directly into their patients - it sort of directs the airflow out and to the sides. Some are made for your own protection, but almost no one wears them properly because it makes breathing difficult. Wearing them properly using involves pinching the metal part at the top over the bridge of your nose. If worn incorrectly, air will come in the sides and especially by the nose.

If worn correctly, masks will protect against both bacteria and viruses. This is not a function of the pore size, however. Bacteria and viruses are transmitted from sneezes etc. in little snot droplets which are then inhaled. The infectious dose for many (not all) bacteria (and I assume viruses, but I'm a little more rusty there) is high enough that you must inhale many (ie a droplet full) rather than a freak influenza particle blown up by a gust of wind.
posted by fermezporte at 9:45 AM on October 19, 2009

By the way, if you're at the point where you're wearing an n95 respirator out in public you might as well go whole hog and wear latex gloves as well. When you're back inside you can peel them off, take off your mask, wash your hands, and bob's your uncle. Of course if you're really paranoid you'd want to take off your clothes before you take your mask off and throw them in the washer immediately and then take off your mask. You can't be too careful.

Please don't do this.
posted by Justinian at 9:50 AM on October 19, 2009

In Japan, surgical masks are worn in order to avoid infecting your fellow humans. How considerate!
posted by halogen at 10:14 AM on October 19, 2009

Ah, here's that article in the NYT that mentions social distancing and surgical masks. It's an interesting thing to consider when wearing a mask: it might help because it keeps other people away, not because it actually works to block the virus from coming in to your lungs.
posted by k8lin at 10:28 AM on October 19, 2009

k8lin, don't take people's looks personally. You have nothing to feel humiliated about when you wear a surgical mask in public. I'm immuno-compromised and wear them in public whenever I have to take public transportation or anticipate being in large crowds. I've been doing this for 5 years now and have only had a few people ask about it. When I notice the looks from people, they're frequently more puzzled than hostile. When people have inquired about my mask, they've been very understanding and pretty cool about it.
posted by onhazier at 10:51 AM on October 19, 2009 [1 favorite]

I have H1N1 right now, and it's looking like it's moving towards pneumonia. I've been given and told to wear (plastic?) lined surgical masks if I leave the house. The masks aren't to protect the wearer, they are to protect people *from* the wearer. I don't know how effective they really are, other than making sure people give you a really wide berth. Also, the nice policemen who stop you when you're speeding home to visit the porcelain gods, will put their lights on and lead you home when you tell them why you're wearing a mask, which is an added bonus, I suppose.
posted by Peecabu at 10:56 AM on October 19, 2009 [1 favorite]