We postulate that there exist three regimes governing the viability of IAV in droplets, defined by ambient RH and shown in Figure 4: (1) physiological conditions (∼99 to 100% RH), where solute concentrations remain at levels harmless to IAV and viability is maintained, (2) concentrated conditions (∼50 to ∼99% RH), where evaporation leads to elevated salt concentrations that may be harmful to the virus, and (3) dry conditions (<50% RH), where solutes crystallize, all water is lost, and IAV viability is maintained.