All salt, by it's nature, is hygroscopic, meaning that it attracts water to
its surface. In a Himalayan salt lamp, this water evaporates quickly due to
the small amount of heat from the light source (this is also why salt lamps
tend to sweat and appear wet in humid climates). Small amounts of water vapor
are present in the air and can carry things like mold, bacteria, and
allergens. Salt lamps attract this water vapor and those items it carries to
its surface and removes them, making air purer.