Negative ions, put in non-scientific terms, are basically oxygen ions with an extra electron attached.
Negative ions are created in nature, when air molecules disintegrate as a result of sun light.
They are also formed as a result of the breakdown of sodium (salt = sodium chloride), a process which means there is a high concentration of Negative Ions in our Salt Rooms.
Negative ions cling and bond with any impurities in the air they occupy.
The impurities (such as dust, mould spores, pollen, pet dander, odours, cigarette smoke, bacteria, viruses and other allergens) become too heavy to stay airborne, and drop to the floor or attach to a nearby surface, so that you are no longer breathing them in.
This prevents the allergens from causing respiratory problems and other health issues.