They have an incredible power to remove dust, pollen, cigarette smoke, and other contaminants from the air. Himalayan salt lamps purify air through the power of hygroscopy, meaning that they attract water molecules from the surrounding environment then absorb those molecules (and any contaminates they're carrying) into the crystalized salt block. As the HSL warms up from the heat produced by the light bulb inside, that same water then evaporates back into the air and the trapped particles of dust, pollen, smoke, etc remain locked in the salt.