Researchers at UC Irvine have found that using fragrant cleaning products while simultaneously using air purifiers that emit even a miniscule amount of ozone pollute indoor air. Emitted ozone from air purifiers react chemically when exposed to volatile chemical compounds such as limonene, which gives cleaning products the scent of lemon. This chemical reaction increases levels of toxic airborne particles in indoor air, which can aggravate asthma, cardiovascular disease as well as increase risk of lung cancer and death. There are many air purifiers that produce high levels of harmful ozone as byproduct of either ionization or oxidization. Ozone pollutants can cause damage to the lungs causing chest pain, sore throat, coughing and breathing difficulty.