Abstract
• Low level carbon monoxide (CO) and heme oxygenase-1 (HO-1) may play a role on the effect of smoking on COVID-19. • CO and HO-1 are anti-inflammatory and cytoprotective and HO-1 is most protective if it is induced before the occurrence of an oxidative insult. • COVID-19 may by itself induce HO-1 and CO which may be potential markers of inflammation or cytokine storm. • Some asymptomatic patients of COVID-19 may have a high baseline level of HO-1 or CO before their COVID-19 infection. • Non-invasive measurement of carboxyhemoglobin using a pulse CO-oximeter may be used to index CO and HO-1 level.