Negative ions are naturally present in our environment from sources such as sunlight, lighting, and waterfalls. These negative ions can even positively affect humans, animals and the environment because they create oases of clean air. However, when it comes to ionic air purifiers, the story is a bit different. Ionic air purifiers are designed to help provide cleaner air and they do so by the use of ionized particles.
While they are very effective at disinfecting air, they should be used with caution, as they can also produce harmful ozone. Inhaling ozone, even in small amounts, can irritate the lungs and cause throat irritation, cough, chest pain and shortness of breath, as well as an increased risk of respiratory infections. A 6-month study found no statistically significant difference in PEFR between active ionization and placebo or non-ionizer environments. Laboratory tests were conducted with particulate air and gas samples in a large semi-furnished chamber and in a field test with an ionizing device installed in an air handling unit serving an occupied office building.
The results showed that an ionizing device led to a decrease in some volatile organic compounds (VOCs), including xylenes, but an increase in others, the most prominent oxygenated VOCs. Another recent study of air ionizers in school classrooms reduced particle concentrations and led to some improvements in respiratory health among children 11 to 14 years old. However, these ionizers had an adverse effect on heart rate variability (a measure of cardiovascular health), meaning that any benefit to the lungs came at a cost to the heart. Ionizer air purifiers are generally safe because ionizers aren't energized enough to be harmful to you.
Since the conflicting data associated with the ionizer remains persistent, it is best to keep the ionizer option turned off unless needed for specific purposes. For example, if you need to get rid of second and third hand smoking from your roommate, you can turn on the ionizer for 30-40 minutes when no one is in the room and then turn it off before anyone comes in.