There is a non-zero risk of aerosolizing bacteria/mold etc if you don't maintain an ultra-sonic humidifier properly, which doesn't exist with other methods. Of

There is a non-zero risk of aerosolizing bacteria/mold etc if you don't maintain an ultra-sonic humidifier properly, which doesn't exist with other methods. Of course with a boiling humidifier, you've got a container of scalding hot water laying around.