You probably think you know how to wash your hands, but Elaine Larson could tell you for sure.

An infectious disease expert who has published more than 200 papers on hand hygiene, Larson is the go-to source for commonly asked questions such as whether anti-bacterial soaps work better than regular soaps (no), whether alcohol hand sanitizer is more effective than hand-washing (yes) and whether you should really wash your hands for as long as it takes to sing “Happy Birthday” twice. (Not necessarily, just be sure to scrub between the fingers and under fingernails.)