This week warning bells sounded throughout the child safety network about the safety of children and the use of ultrasonic humidifiers.  This time it's not just due to possible exposure to fire incidents (although on January 11, 2011, the CPSC issued a voluntary recall of 198,000 GE and Professional Series humidifiers due to a possible fire hazard in those makes and models).  It is believed that the ultrasonic humidifiers release tiny particles into the air from the water used in the humidifier. The amount and type of particles is largely dependent upon the minerals in the water.  Simply put, there have been concerns that babies may breathe in air containing minute particles and a concentration of these particles may harm a baby's lungs and/or the lining of a child's nose and airway. 

The Environmental Protection Agency, as early as 1991, issued guidelines on the "Use and Care of Home Humidifiers" noting that the moisture released into the air by the humidifiers could encourage the growth of biological organisms (including dust mites and molds) in the home. 

"Studies by the Environmental Protection Agency (EPA) and the Consumer Product Safety Commission (CPSC) have shown that ultrasonic and impeller (or "cool mist") humidifiers can disperse materials, such as microorganisms and minerals, from their water tanks into indoor air."  At that time, it was noted that "only limited information was available on the growth of microorganisms and the dispersal of microorganisms and minerals by home humidifiers." http://www.epa.gov/iaq/pubs/humidif.html   

In addition, it was noted at the time that "minerals in tap water may increase the development of crusty deposits, or scale, in humidifiers. Scale can be a breeding ground for microorganisms.  One way to reduce the possibility of emitting particles is to use distilled water which already eliminates much of the mineral content in "hard" water.

It was noted that it is extremely important to keep humidifiers clean. Regular cleaning daily and once a week disinfecting were recommended to minimize dispensing biological organisms and molds into the air.

Because some humidifiers use a heating element to create steam, hot water and steam can create scalding hazards to young children.  So childsafetyblog.org  recommends keeping steam models away from small children.