Autopsy reports have revealed copious amounts of a gray-white viscous fluid in the lungs of COVID-19 patients.15,16 Consistently, protein exudates were also observed in a COVID-19 patient diagnosed following lung cancer surgery.17 In addition, a new study from single cell sequencing reported mucin expression in lung epithelial cells of COVID-19 patients.18 These observations prompted us to hypothesize that SARS-CoV-2 infection stimulates mucus production, thus promoting hypoxia by hindering O2 diffusion at the alveolar sites. Here, MUC5AC is linked to COVID-19.