The CDC is reconsidering its policy about the widespread public's use of masks, as is the World Health Organization. Here are the facts about when it's appropriate to wear a mask – and what kind.

Harvard researchers have devised what they hope is a better way to disinfect hands, using tiny aerosolized nanodroplets of water and nontoxic disinfectants that not only leave hands sterile, but use so little water the hands stay dry.

Harvard’s Keutsch Research Group is working on a controversial idea that might someday be our best hope against climate change: stratospheric aerosol injection.