QUESTION
Is it safe to burn mosquito coils inside? What's in them? What constitutes "prolonged inhalation," which the package says to avoid?

ANSWER

To answer your first question first: No, mosquito coils are not intended for use indoors. The labels and directions for use on all the brands available for sale in Canada (which read much alike, since their wording is mandated by the Pest Management Regulatory Agency, or PMRA, a division of Health Canada) say, in effect: "Use in confined outdoor areas such as porches, covered patios, and other areas where there is little movement of air." Used in such sheltered areas, they are effective, able to both kill mosquitoes (by paralyzing their nervous systems) and act as a repellent, explains PMRA toxicologist Brenda Linke. But they don't work very well on an open deck or in any kind of a breeze.

The active ingredient in a mosquito coil is either natural pyrethrin or a synthetic version known as a pyrethroid (both referred to generally as pyrethrins). Natural pyrethrins are extracted from the flowers of some members of the daisy family - usually Chrysanthemum cinerariaefolium, a.k.a. the Dalmatian daisy. An improved, more potent strain of this plant, originally native to eastern Europe, is now grown in mountainous regions of Kenya, Tanzania, and Ecuador, specifically for use in a wide array of house and garden insecticides, including mosquito coils.

The reason pyrethrins are so common in home-use pest products is their low toxicity to both humans and domestic animals, according to the PMRA. Pyrethrins are relatively harmless if ingested, producing no harmful residues on food, and readily broken down by sunlight and air. That doesn't mean you can use the coils carelessly. The labels variously advise, without getting too specific about it, that you should "avoid inhalation of smoke" or "avoid prolonged inhalation." This means that if a coil lasts seven or eight hours you shouldn't - and probably wouldn't need to - light another one, says the PMRA's Linke. According to Gord Surgeoner, a medical entomologist at the University of Guelph, the biggest concern - apart from the fact that inhaling smoke is never a healthy thing to do - is the possibility of mild allergic reactions such as sneezing or a runny nose.

* Published in the April/May 2002 issue of Cottage Life