Earlier quoted context omitted.
They don't work? This article is claiming otherwise: https://www.nature.com/articles/d41586-020-02801-8
It's quoting a whole lot of things, some of which are in support of cloth masks, but none of which are particularly conclusive. It's worth noting that one of the randomized trials mentioned in that article ended up not being able to prove any significant effect. [1] It apparently had some problems getting published. I've been unable to find the results of the larger trial by Christine Benn et al. [1]: https://www.acp…
https://advances.sciencemag.org/content/6/36/eabd3083
I understand we also want RCTs to show that they actually reduce infections in practice. But, I will note a few things here.
It's almost impossible to study via RCT whether their usage protects other people from infection, which is one of the goals of masks. The best we can do is go with our knowledge that it does block aerosols from being exhaled and use common sense to then assume that this means that it also will protect others from getting infected.
Also, it could be the case that while it may not prevent infection, it reduces the severity of the infection due to a much lower viral load being inhaled. This is a difficult question to study.
In all, we need to see larger studies done in locations where there's more cases. That one RCT in Denmark isn't enough.