Harlan Krumholz

So it's interesting.

I mean, the evidence in this area is right, is it tends to be a dearth.

There's been a few randomised trials recently, but the Cochrane review here on physical interventions to interrupt or reduce the spread of respiratory viruses is, first to say, quite old.

It's not been updated since 2011.

But in there, there are a mixture of case control and cohort studies.

And in there, there are case control studies that have looked at mask wearing.

And they looked at two types of masks, surgical masks and these N95 respirators, which cost more money.

And you can find them available at the moment on the web, but the price is going up.

But what's interesting about them is both of them, across eight studies, generally led to about a two-thirds reduction in infectivity.

But also to say that most of them studies were combined with frequent, the word is frequent, hand washing.

And so teasing the different bits out can be difficult sometimes.

So I think if you're going to wear a mask, you've also got to do the frequent hand washing.

Well, generally in the studies, it's at least five times a day.

And one of the things is...

No, but one of the things is some people with soap, and that is reported in some of the studies, might find that an irritant because of certain allergies and eczema.

So some people do report them irritants.

Also, the thing about the N95 respirator masks is...

Although I said they were more expensive, people reported them as more uncomfortable and they were more irritated to the skin.

And so that comes back to this point about what she said.

A really important point is this intention to treat analysis.