In South Korea they have been struggling with a stealth enemy that has penetrated home defenses and lethally attacked innocent civilians. This is not the result of an evil plot emanating from the other side of the demilitarized zone. Rather, it seems to have been the result of untested chemical agents widely sold and commonly used to kill germs in home humidifiers.

Beginning in 2006, the Koreans began to notice a rare but devastating syndrome of severe lung injury occurring in very young children, typically at about two and half years of age. More than half the children afflicted succumbed to this mysterious illness, which included rapid onset of lung scarring (fibrosis). At first, it seemed that this might be some new and terrible viral pneumonia, but doctors failed to implicate any microbe as a cause of the epidemic. The spike in cases typically occurred over a few months each. No one knew why.

Then, in 2011, the biggest spike yet in childhood cases occurred. The same spring in Korea, there was another outbreak of a very similar and frequently fatal lung disease with many of the same characteristics, only the victims were an entirely different risk group: pregnant women. That outbreak was concentrated enough that an epidemiological investigation revealed its like cause. The women affected were much more likely to have used humidifiers in their rooms and to have added chemical agents to them. These chemicals were “biocides,” intended to keep down bacterial growth in the humidifier water.

Biocides are chemicals that kill microbes in the environment. For good reason, these substances are categorized more broadly as being a form of pesticide (along with insecticides and herbicides, as two other examples). In the outbreak among the pregnant cases, there were multiple different synthetic materials (among twenty or so on the market) that were the most strongly implicated. All have complex chemical formulae with simple initialized names that make them sound benign; the two most highly suspect are known as PGH and PHMG (

What the Koreans did next was take a step that almost never happens quickly in the U.S.: in November of 2011 they banned outright the chemicals that they believed had killed the pregnant women. They also suspected that these same biocides might be the cause of the infants’ illnesses as well. The suspicion was confirmed when in the spring that followed the ban the annual uptick in cases did not happen. In fact, there has not been a single case since. When Korean epidemiologists later studied the prior childhood cases in depth, they found that for one in five there also was an adult in the household who had been ill, too.

A year ago, the Finns acted to ban PMHG, which made healthcare workers there happy, since Finland had been looking at its use as a hospital disinfectant; the workers are less happy that PHMB, a related biocide which makes up the backbone of PMHG when made into a long polymer chain, is still allowed ( This past September, the European Union put new regulations in effect specifically mean to strengthen controls on biocides as a class   ( Meanwhile, you can still purchase PMHG: if you are interested in a big drum of the stuff, check out the Taizhou Sunny Chemical Co. As they say on their website, “PHMG can be used for decontamination and resistance of microbe, including bacteria, virus, fungi, mildew and algae; in the field of medical use, hygiene, textile, wet-tissue, fishery, planting, food-processing, water treatment etc.” I guess inducing fatal pneumonia falls under etcetera.  (

How about in the U.S.? In investigating their outbreak, the Koreans naturally turned to see what the U.S. Environmental Protection Agency (EPA) thought about these products. They noted that the U.S. had never approved the use of PHMG in an inhalable form but it had reviewed it precursor PHMB for its acute and chronic dietary risks and found it was “below the level of concern” (

OK to eat, I guess. Just don’t get caught up in the fog of war when it comes to the facts on pesticide safety.

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