Since new coronavirus disease (COVID-19) caused by SARS-CoV-2 was first reported in China, recent studies proposed a potential relationship between PM2.5 concentrations and the severity of SARS-CoV-2, which might be closely associated with altered expression of ACE2, the entry receptor for SARS-CoV-2, by chronic exposure to PM2.5. This evidence concerns the gene ACE2 and COVID-19.