Since the start of the COVID-19 pandemic there has been much debate in the media on whether masks should be worn to stop the spread of the virus. There are two ways in which they could work. Firstly, to protect the person wearing the mask, and secondly, to reduce the likelihood of the person wearing the mask passing the disease on to anyone else. This is not an easy issue to address and many factors come into play such as droplet size, aerosol transmission and the viral load, as well as the specific properties of any given mask. The method used in this study was to measure the change in relative humidity when wearing a mask, compared to no mask, in various scenarios, based on the assumption that as the virus is air-borne the smaller the increase in humidity the less the spread of the virus. The results above show that the use of a mask, excluding some simple home-made ones, significantly reduces the spread of humidity. However, their effectiveness is device specific and needs to be considered in greater detail for each type of mask, especially the direction of escaping air when forward flow is blocked.