During the H1N1 influence pandemic of 2009, microbiologists warned that the distance and duration that a wand is held from an infected surface are both critical. But the surface itself matters, too. Smooth surfaces like marble and glass are easier to disinfect than wood or cloth.
In 2015, the Federal Trade Commission went after two companies marketing UV disinfectant devices because of false claims about eliminating foot fungus, methicillin-resistant Staphylococcus aureus, E. coli and Salmonella.
UV-C’s germicidal powers depend on the dose — how much optical energy the source delivers, the distance from the source and time of exposure, says Christian Zollner, a materials scientist at the University of California, Santa Barbara. Plus, most of the wands use LEDs, which are less efficient for disinfection, says Zollner.