Inhalation or exposure to negative ions is quite safe for humans, since negative ions are already naturally present in our environment from sources such as sunlight, lighting, and waterfalls. However, it is the ozone production of these ionic air purifiers that poses a risk to human health. Inhaling ozone, even in small amounts, can irritate the lungs. Specific effects may include throat irritation, cough, chest pain and shortness of breath, as well as an increased risk of respiratory infections.
Air ionizers are designed to help provide cleaner air and they do so through the use of ionized particles. Ionizer air purifiers are generally safe because ionizers aren't energized enough to be harmful to you. These ionizers turn on for 8 hours every day, and I have a Therapure TPP300D with UV+ ionizer that turns on for 8 hours in my living room. Since the conflicting data associated with the ionizer remains persistent, I usually keep my ionizer option turned off.