Just how safe are mosquito coils?

Walk down the main street of any tourist-town in Southern Thailand and you will likely find a mosquito coil smoking away under every table in just about every restaurant. The tourist wonders: is mosquito coil smoke hazardous to my health?

Travelers seem to fall into two camps on this issue. Some worry about it and try to avoid the mosquito coil smoke; others dismiss the health concern, considering the smoky coils a prudent precaution to thwart insects and the serious diseases they may harbor, most notably, dengue fever and malaria.

Jotman investigates.

According to a study by UC Riverside scientists, many mosquito coils – most notably those manufactured in Asia – often contain up to one percent BCME (which stands for bis[cloromethyl]ether, a chemical associated with the breakdown of S-2). BCME has been described as “the most potent lung cancer chemical ever discovered.” And lung cancer is just about the most deadly cancer known. In one Chinese factory where mosquito coils were manufactured, a large fraction of employees were dead within five years of starting their jobs. The cause? Lung cancer.

By contrast, no study of cigarettes has ever found tobacco smoke to pose any where near such a high risk. Put it this way: there is no comparison between cigarettes and mosquito coils. Another study -- one that only considered the amount of "small particulate matter" present in mosquito coil smoke (it did not investigate BCME question) -- found the coils to be about 100 times more hazardous to human health than tobacco smoke.

It is illegal to sell mosquito coils in the United States that contain BCME. Nevertheless, Chinese-made mosquito coils that contain BCME have penetrated the US market in recent years.

What to do about the risks associated with mosquito bites; the very real threat of contracting insect-born diseases like dengue and malaria? Mosquito bites can and should be prevented by each individual taking some basic personal precautions:
  1. In the evenings or wherever mosquitoes are prevalent during the day, keep your body covered in light-colored clothing and spray insect repellent onto exposed extremities.
  2. At night either sleep under a mosquito net, stay in room with well sealed mosquito screens, or sleep in an air-conditioned room.
  3. Remember: malaria-bearing mosquitoes strike in the evening and at night. Dengue-carrying mosquitoes can strike at any time.
Burning a mosquito coil while you sleep is not a good idea. Mind you, this is exactly what Thai TV commercials urge the locals to do: one such advertisement shows a group of smiling Thai kids singing about virtues of mosquito coil smoke. Mosquito coils are a big business in Southeast Asia; companies with ties to corrupt governments are not about to let a real health hazard stand in the way of real profits. Whether you are a local, tourist, traveler, or foreign resident of Southeast Asia, it’s better to think for yourself and not blindly follow this mass-media dictated local custom. For as a UC Riverside research team concluded:
In many situations, it seems likely that the reality of mosquito-borne diseases (Mulla et al. 2001) may dominate determination of hypothetical risk:benefit ratios for mosquito insecticides delivered using devices such as coils. However, if BCME were an important environmental contaminant resulting from burning mosquito coils containing S-2, it would be impossible to maintain use given the well-established carcinogenicity of BCME in humans.
Translation: the risks associated with BCME are so incredibly high that even the contribution mosquito coils make towards stemming the world’s worst tropical diseases would not seem to outweigh the hazard.

My conclusion: Mosquito coil smoke is highly toxic to humans and should be avoided.

25 comments:

  1. Good one!!!
    Thank you for answering and questionig.
    I have been using mosquito coils for years. I am now going to stop it.

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  2. Wow, I remember using mosquito coils in the Philippines many years ago. Is it ok if I write about your post in my blog? I will put a link to your blog.

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  3. Babette - sure. It's good that you will help spread the word about this stuff.

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  4. Is it only coils containing BCME? Can you buy coils without this? I am living in Spain and left the door open last night - I am covered in bites today!!

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  5. Hi Paul,

    It is likely that some coils do not contain BCME, but how could we know the difference? Most such products having been either made in China, or containing materials sourced from China....

    In Spain mosquito bites are unlikely to give you any serious disease, so I can't imagine why it would be worth the risk to experiment with the coils and their mystery ingredients.

    Instead, why not try out eucalyptus-based mosquito repellent?

    http://thejotazine.blogspot.com/2007/02/are-there-natural-alternatives-to.html

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    Replies
    1. what are the medicinal purposes of mosquito coil?

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  6. Could you cite a source for the following passage?: "In one Chinese factory where mosquito coils were manufactured, a large fraction of employees were dead within five years of starting their jobs. The cause? Lung cancer." If true, it's intriguing because BCME is presented as a combustion by-product in the UC Riverside paper. Thus, the paper doesn't obviously apply to the vapor-releasing "mats" which are electrically heated rather than burned. These have largely supplanted the smoldering coils in Japan. Presumably they're not burning the compounds in the factory, so the fact that they got cancer there anyway may give reason for concern beyond just the coil-type repellents. Of course, who knows what's going on inside the factories; they may be exposed to levels of repellent way beyond that of a consumer, or might be exposed to some catalysis agent that doesn't even make it into the final product. Again, a citation would be useful here.

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  7. Matthew,

    The link above (which no longer seems to work) was the source of the information about the 5 workers.

    The same case is mentioned here:

    Zhang, Xiaofei,"Octachlorodipropyl ether (S-2) mosquito coils are inadequately studied for residential use in Asia and illegal in the United States." Environmental Health Perspectives, 2003

    The potency of BCME was also evident in a small factory in China. There, 5 of 15 workers exposed to BCME during S-2 manufacture were diagnosed with lung cancer. Four of the workers were younger than 40 years (Xue et al. 1988).

    Another quote from the same study:

    ...a rare form of lung cancer (primarily small cell undifferentiated), occurred in 12 of 13 persons occupationally exposed to BCME and CMME.

    Your question how, if BCME is released during combustion, would this impact the factory workers? Concerning the amount of exposure needed to cause cancer the study reported:

    Studies in rats and mice have shown that 0,1 ppm or 1 ppm of BCME in air, respectively, induced lung cancer. . .

    Perhaps in routine storage and handling with an enclosed factory space enough of the S2 oxidizes and gets into the air. Certainly the danger posed to consumers could well be several orders of magnitude greater to that posed for factory workers who are presumably not breathing smoke!

    As for the rats,

    Severe shortening of life span was seen in 30-day exposures of rats to CMME and in all studies with BCME.

    Drew RT, Laskin S, Kuschner M, Nelson N. 1975, "Inhalation carcinogenicity of alpha halo ethers. I. The acute inhalation toxicity of chloromethyl methyl ether and bis(chloromethyl)ether." Feb;30(2):61-9., Arch Environ Health.

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  8. Going to have to go and play devil's advocate here. I am in no way downplaying the effects of mosquito coils and their potential toxicity. But I do know for a fact that my mother and her relatives have burned coils throughout their lives before the S2 crisis and not ONE of them have any rare form of lung cancer. As a matter of fact, they and their friends and relatives live well past the ages of 80 and 90.

    At worst we do have allergies but that happens regardless of the coils.

    Also, S2 has been noted and addressed in Hong Kong. http://www.afcd.gov.hk/english/publications/publications_press/pr553.html

    The coils we are burning now bought in the borders of Hong Kong and China even state how it does not have S2. You basically want to be sure that the products you buy don't have that. But on that note, if you don't practice common sense ventilating the area and not burning it all day more than at dawn and dusk, you shouldn't be using the coils at all.

    You'd be surprised how many toxic goodies are found in normal, us made household products such as soap and detergent. And when used in LARGE amounts you'd die from them as well. So if you don't know how to use a coil don't.

    That said, we use these smelly coils in short durations. The locals here prefer to use a coil in 2-4 hour sessions and when the room smells sufficiently of the stuff we just extinguish it. This does the job of warding of the skeeters and giving us prevention from dengue, malaria and other fun illnesses.

    So to walk on eggshells for something that might happen if I breath nothing but S-2 coil smoke all day is honestly being paranoid.

    True, Lung Cancer is a major killer her but far more potent than coils is direct smoking (which locals love to do) and of course the awful and hideous toxic industrial air pollution that cripples BeiJing, Hong Kong and Shenzhen. We'd die from air pollution long before we'd die from burning a mosquito coil daily during summer.

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  9. what a fear mongering hack. disrespectful to victims of diseases, you're saying contracting malaria/dengue fever is better than using a mosquito coil!!!!! quote:"the contribution mosquito coils make towards stemming the world’s worst tropical diseases would not seem to outweigh the hazard" ok sure, if i sucked on a pack of coils a day i would be in trouble. but the only time you need coils is when there is a window open or you're outdoors--- hence VENTILATION.
    does the word EVIDENCE mean anything to you? pls may i see references for the maniacal accusations such as "coils that contain BCME have penetrated the US market in recent years." "companies with ties to corrupt governments"
    article is piece of comedy, not journalism.

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  10. Bob,

    One important point here is that mosquito coils aren't all that effective anyway. Anyone serious about preventing malaria/dengue should turn to that which has been proven effective: mosquito nets and protective clothing. Malaria/dengue are serious diseases and coils are not an especially effective means by which to protect yourself.

    Do you honestly believe that Chinese factories (where most mosquito coil get made) put only EPA approved chemicals that are safe to breathe into mosquito coils? On what basis do you reject the scientific studies I have cited? It seems you would give the Chinese factories the benefit of the doubt.

    Don't you follow the news? Everybody knows that Chinese factories have put lead in children's toys, heavy metals in beauty products, deadly contaminants in Chinese-made toothpaste. There's the tainted milk scandal. Have you heard about the fake malarial drugs? Guess where they are made!

    What evidence do you have that made-in-China BCME containing coils have NOT penetrated the US or any other market? We can't assume it's safe to breathe any combustable product likely to have been made in China. Today, given such a reckless track-record, the burden of proof is with those who would assert the safety of any such product.

    Show me your evidence.

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    Replies
    1. I have lived in the tropics my whole life, every year there is a dengue out break. My home does not have screens and we burn 2 coils, every morning and evening. You are not suppose to breathe the smoke in, it should go down wind from where you are as this is how the mosquitos find you, they come up wind in the carbon dioxide your body releases. What about DEET directly on your skin being absorbed by your largest organ, the warning is on the packet "May be dangerous when used for prolonged periods of time" - Truth is mozzies kill millions of people every year, they are the most dangerous animal on the planet. Coils are cheap, effective and they do work!

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  11. Thanks for the blog you've made Mr. Jotman.
    I am a student here in the Philippines. We have a project in regards to developing our own mosquito coil that is new to the public. I was wondering if there are good attributes of a mosquito coil that will not harm the users than the traditional mosquito coil which has BCME? Thanks!...

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  12. I wonder if not all of the mosquito coils in the market is bad? Some includes dl,d-T80-allethrin and may not harm.
    I would be grateful if you could have your opinion on this article:

    http://www.ncbi.nlm.nih.gov/pubmed/19842376

    [Southeast Asian J Trop Med Public Health. 2009 Sep;40(5):929-36.]

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  13. This is really good articl. I live in Bangladesh (southeast asia) and have been using mosquito coil during sleep time for ten years. I went to hospital for my chest X-Ray (which is mandatory by British High Commission for those who want to go to UK) in two times in the gape of one year because I was going to London for study and each time a small spot is caught but doctor said its not a problem. They are testing TB thats why I wasn't enough worry about it.

    After reading this articl, I'm really afraid of getting lung cancer. What should I do? Please give some advice.

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  14. Baygon has proven that their coils are very safe and effective in killing mosquitoes and other insects. They've also included scented coils in their product line which is quite unique.

    Pest Exterminator

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  15. Baygon has proven that their coils are very safe and effective in killing mosquitoes and other insects. They've also included scented coils in their product line which is quite unique.

    Pest Exterminator

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  16. I've always put a mosquito coil in my tent before I go to sleep because those Blackflies in northern canada are very bad but I put them in my tent before I go to sleep and I'm 13 and 6 feet tall so I think im ok so far !

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  17. I am extremely sensitive to mosquito bites, and swell up and itch like crazy. Since I discovered them I've used coils for 10 YEARS or more, and if used according to directions I absolutely believe it is better than swatting and getting bit and itching and not being able to work out in your backyard. Read the ingredients of the spray repellents. And you are puttin that stuff directly onto your skin. You don't think you are absorbing that into your system? Granted I'm in a climate that snows part of the year, but still I believe worth it. Maybe those who have to burn them continuousy should wear masks too.

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  18. Ever gone camping in the woods where there are no porta potties? I don't know of any netting that will cover you when you're doing your duty in the woods. ever get bit down there? have fun explaining why you're scratching your privates the rest of the time. So you can either take a can of spray in the woods to scare the critters off for a few minutes, and breath in those fumes, or take a burning coil with you, or get bit on the butt.

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    ReplyDelete
  20. I inhaled some coil smoke and now i am having itchy throat since 2 days

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  21. Just sprayed my home indoors with a natural brand of citronella and eucalyptus for deterrent to puppy urinating smells nice but strong does anyone know if it is safe for humans to breathe it.

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  22. Just sprayed natural product of citronella and eucalyptus in house to deter puppy urinating on furniture .smells nice but strong is it safe for humans to breathe.

    ReplyDelete