Dr. Anthony Fauci was asked about whether or not it made sense to wear two masks, and said,
We get asked all the time, should we be double masking? The CDC makes recommendations based on data that they accumulate because it’s a science-based organization. Right now they are looking at these different options of mask-wearing. In the meantime, as I often get asked, should you be wearing two masks or one mask? And I say, there’s no recommendation. However, there are many people who take the common sense approach. If you’re talking about a physical barrier, and as the CDC recommends, you want at least two layers within the mask as a physical barrier, and you feel maybe more of a physical barrier would be better. There’s nothing wrong with people wearing two masks. I often myself wear two masks. Can we make a general recommendation that doesn’t have scientific basis yet? No. But when the science comes along and tells us that it is better or not, then you will see a recommendation being made by the CDC.
Personally, I have taken to wearing two masks whenever I am in a situation where there are likely to be a lot of people around, such as while grocery shopping. I typically wear a single-use, three-layer mask and then a cloth mask over the top of that. Along with any (as yet unproven) benefit to wearing two masks, it also helps the disposable mask have a tighter fit around the edges of my face.