An ionizing agent is a device which ionizes molecules, meaning it creates an electric charge on parts.
In general an ionizing agent is a device which can be used at home for example to reduce the amount of dust particles in the air. This principle is also used for cleaning exhaust fumes and removing dust in long tunnels; this is usually called an electrostatic precipitator.
One of the ways to ionize the air is to make sure the device ‘sprays’ electrodes in the air by putting a needle under a negative high voltage. The electrodes will attach themselves to oxygen molecules. There are two theories which discuss what will happen next: According to one theory the charged oxygen molecules attach themselves to dust particles in the air and end up in the environment as they are electrically charged. According to the other theory harmful dust particles are positively charged which is neutralized by the negatively charged oxygen molecule.
A needle is usually used to simplify the process for electrodes to end up in the air. The electrodes jump off the needle from the very end of it. The needle is under a few thousands volts. As voltage is very low, it is not dangerous to touch this needle.
There are various opinions on the amount of dust the device extracts from the air. It strongly depends on other factors, such as ventilation. It is unknown, whether and to what extent reduction of the number of dust particles will influence healthy positively and if it would apply to all people or just to people with certain allergies.