Having researched air ions before, I can attest that the subject is extremely technical and, worse, often prone to contradiction and obscurity depending on who is writing (and who is selling) various ideas. It is another of those interdisciplinary areas with different and competing claims, in this case, from fields as divergent as air chemistry, ecology, and human health. The following article, from Townsend Letters, does an admirable job of introducing most of the major competing health claims and sifting the evidence:
Static Electricity and Respiratory Infections
More times than not, shaking out a blanket on a cold night generates the crackle and sting of static electricity and a flurry of sparks. Synthetic materials, low humidity, and ungrounded electrical equipment are producing an unprecedented amount of electrostatic charge indoors, and these electrical fields may be contributing to increased risk of respiratory illness and other infections, according to a 2007 article in Atmospheric Environment. Indoors, most particles, including microbes and allergens, are so small (less than 1 microgram) that they could float in the air indefinitely; but electrical charges cause these miniscule particles to settle on surfaces and stick. These surfaces include skin and lungs. High electrostatic levels and increased deposition of airborne particles on skin have been linked to facial rashes, especially when humidity is low. Charged particles in the lungs increase the risk of infection and asthma.
Keith S. Jamieson, H. M. ApSimon, and J. N. B. Bell advocate several ways to decrease indoor static electricity and the accompanying health effects. One recommendation is to reduce electrical charges by grounding laptop computers and other electrical equipment. They also recommend unplugging equipment when it's not in use.
Another option is bipolar air ionization. (Long-term unipolar air ionization with negative ions has shortened lifespan of laboratory animals.) Air ionizers produce varying amounts of ozone, which damages the lungs, according to the EPA. Jamieson et al. urge people to use passive air ionization measures, such as grounding electrical equipment and choosing materials and furniture finishes that do not conduct electrical charges.
Another way to combat electrostatic is to use humidifiers. Indoor heating and cooling systems often reduce humidity levels. Low humidity encourages high electrostatic levels and decreases beneficial small air ion levels. (Small air ions kill microbes and reduce employee fatigue in the office workplace.) Humidifiers are often used to make breathing easier during respiratory infections; but humidifying indoor air, especially in winter months when furnaces are running, may prevent illness as well.
Jamieson KS, ApSimon HM, Bell JNB. Electrostatics in the environment: how they may affect health and productivity. Electrostatics 2007 Journal of Physics: Conference Series. doi:10.1088/1742-6596/142/1/012052. Available athttp://iopscience.iop.org/1742-6596/142/1/012052. Accessed September 18, 2012.
Jamieson KS, ApSimon HM, Jamieson SS, Bell JNB, Yost MG. The effects of electric fields on charged molecules and particles in individual microenvironments [abstract]. Atmosph Environ. August 2007;41(25):5224–5235. Available at www.sciencedirect.com. Accessed April 27, 2011.
Reeves D. Electrical fields from everyday equipment and materials could increase infection risk [press release]. Imperial College London. July 20, 2007. Available atwww3.imperial.ac.uk. Accessed September 18, 2012.