Early in the COVID-19 pandemic, doctors recognized that patients who developed a “cytokine storm”—a surge of pro-inflammatory immune proteins—were often the sickest and at highest risk of dying. But a cytokine storm can also occur in other illnesses, such as influenza. Today, scientists report preliminary results on a sweat sensor that acts as an early warning system for an impending cytokine storm, which could help doctors more effectively treat patients.