Product review (5 stars): Clean Cool Mist
Using a product like this in your humidifier is a little extra added assurance that the cool vapor from your unit is as sanitary and clean as possible.
A very popular new product is an essential oil diffuser. The diffusers operate in much the same way as any humidifier, with the exception that you can place a drop of essential oil to scent the air. Bacteria is just as common in those types of units as they are in any humidifying device.
I've been using this solution in those small oil diffusing products, and there are no adverse effects.