Researchers suggest that men may be more prone to getting COVID-19 (or experiencing severe symptoms) because men in China tend to smoke more than woman (288 million men versus 12.6 million woman in 2018). One study found that ACE2 expression was significantly higher in current smokers of Asian ethnicity as compared to Asian non-smokers. Although intriguing, no concrete conclusions can be drawn about this hypothesis, because, so far, it lacks strong evidence.