A study that was designed to investigate how the immune system impacts gut bacteria has led to the discovery that two molecules, L-tyrosine and a metabolite, p-cresol sulphate (PCS), can not only provide profound protection in experimental models of asthma, but can also substantially reduce the severity of an attack. Further animal studies suggested that the molecules may have a potential role in treating acute respiratory distress syndrome (ARDS), the sometimes fatal respiratory illness that can develop in people with serious COVID-19.