Karen Walsh is the Professional Education Team Leader and Clinical Scientist at the Centre for Ocular Research & Education, (CORE) based at the University of Waterloo, Canada. She has previously worked as a Professional Affairs Manager in the contact lens industry, and in clinical practice in the UK. She holds a post graduate diploma in Clinical Optometry from City University, London UK, and is a Fellow of the International Association of Contact Lens Educators and the British Contact Lens Association.
Use of face masks is becoming more common around the world. This study sought to examine, via video visual representation, the efficacy of different mask designs in reducing expelled aerosols from the mouth and nose.
Face coverings and mask to minimise droplet dispersion and aerosolisation: a video case study
Prateek Bahl, Shovon Bhattacharjee, Charitha de Silva, Abrar Ahmad Chughtai, Con Doolan, C Raina MacIntyre. Thorax 2020;75:1024–1025.
Using a healthy subject, four conditions were examined: no mask at all, a one-layer cotton fabric mask, a two-layer cotton fabric mask, and a three-ply surgical mask. With each condition, high speed video was used to capture light scattered by droplets and aerosols when speaking, coughing and sneezing.
For speaking, a two-layer mask performed better than a single-layer cloth mask, which in turn was better than no covering at all. When coughing and sneezing, a double-layer cloth mask was significantly better at reducing the droplet spread compared to a single layer mask or nothing at all. In all conditions, the surgical mask was the best in preventing droplet spread from any respiratory emission.
Take home points: The videos demonstrate the value of using face masks in general, and of the difference in efficacy between different types of masks. There are additional factors that contribute to overall mask efficacy, including material type, the number and type of layers, the fit of the mask and how often it is washed. The videos show that for cloth masks, a design with at least two layers is preferable to a single-layer. Where available and necessary to use, surgical masks reduce droplet spread most efficiently out of the types tested in this study.