Product review (2 stars): Caution on the use of Quaternary Ammonium Chlorides/Compounds (QAC)
Conscientious consumers and parents might want to do some research before using this product in a humidifier, particularly if family members have asthma or other respiratory disorders.

The active ingredients quaternary ammonium chlorides (QAC)are a member of the benzalkonium chloride class of chemicals which the Environmental Working Group (EWG), in a letter to the EPA objecting to a roll-back of safety standards in food preparation settings, states are widely recognized asthmagens and potential reproductive toxicants used in a broad range of commercial and household cleaners and other consumer products. http://www.ewg.org/news/testimony-official-correspondence/epa-proposes-roll-back-food-safety-standards-request

Although this letter of objection does not refer to the dangers associated with aerosolization of these chemicals, numerous studies suggest that QACs and other similar chemicals are respiratory irritants and/or hazards:  "The use of these materials in spray products and plug-in air freshener products is particularly worrisome in terms of increased chemicals in the air and exposure to both the persons using the products as well as the individuals who are using the space. A recent CDC report considers disinfectant spray-fog technique to be an unsatisfactory method (5). " http://www.oem.msu.edu/userfiles/file/News/v20n1.pdf

Here are links to additional studies referencing the hazards of these chemicals when they are inhaled:

Pulmonary irritation after inhalation exposure to benzalkonium chloride in rats. 2008
http://www.ncbi.nlm.nih.gov/pubmed/18715840

Toxic effect in the lungs of rats after inhalation exposure to benzalkonium chloride. 2013
http://www.ncbi.nlm.nih.gov/pubmed/24288119

Obviously the poison is in the dose, but with no information provided on the bottle regarding how much QAC are in the recommended amount and the degree to which the QAC may be aerosolized through its usage, it might be prudent to err on the side of caution.