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Heat-Not-Burn Cigarettes: Study Shows More Research is Needed

The Tobacco-Related Disease Research Program (TRDRP) has long supported research into the health effects of novel Electronic Nicotine Delivery Systems (ENDS) such as electronic cigarettes.  As early as 2011, TRDRP sponsored grants to investigate the components of these devices and the risk they pose to human health.

Interest in developing ENDS products that expose cigarette smokers to fewer toxic chemicals has led to the development of “heat-not-burn cigarettes.” Rather than burning tobacco to deliver nicotine, a rolled cast leaf sheet of tobacco is heated to about 300oC, a temperature that does not cause burning but is high enough to create an aerosol containing nicotine that can be inhaled by users.  One heat not burn product, iQOS, which was introduced several years ago, has been marketed successfully by Phillip Morris International in over 31 countries. iQOS, which some say stands for “I quit original smoking”*, is not currently marketed in the United States. The FDA’s Tobacco Products Scientific Advisory Committee recently found that iQOS reduced smokers’ exposure to harmful chemicals but said the company had not proved conclusively that it would result in less harm and disease.

In research conducted by the manufacturer, Phillip Morris International, it was shown that harmful, and potentially harmful chemicals (HPHC) are reduced in iQOS aerosol.  However, relatively little research has been done on this product by independent investigators. Recently, Barbara Davis and Monique Williams (pictured on the right), and Prue Talbot, with support from TRDRP, published an evaluation of iQOS in the journal Tobacco Control.  They found the product to be well manufactured and to have similar performance properties when comparing different units and different heatsticks, unlike other ENDS products, which can be highly variable between units. However, iQOS had certain performance characteristics that will likely affect how it is used, to the detriment of human health. First, iQOS can only be operated for 6 minutes at a time, after which it shuts off and needs to be recharged. This constraint may cause users to decrease the interval between puffs so as to get the most from each heat stick.  By decreasing the interval between puffs, users will likely inhale increased amounts of nicotine, as compared to other ENDS products.

Second, iQOS requires cleaning which the manufacturer recommends be done after every 20 heat sticks.  This is intended to remove fragments of the cast leaf tobacco and liquid residue that accumulates in the heating chamber. Davis et. al. observed that although the iQOS tobacco does not combust (burn), it undergoes pyrolysis (the process of heating an organic compound in the absence of oxygen) and appears charred around the heating element after use. Interestingly, the zone of charring was substantially larger when cleaning was done as recommended by the manufacturer, in contrast to when cleaning was done after each stick. This suggests that without regular cleaning, temperature in the heating chamber increases leading to more pyrolysis and charring of the tobacco.  Pyrolysis and charring of tobacco has been shown to release chemicals that are toxic when inhaled.

Third, the authors observed that the polymer-film filter that is used to cool the aerosol before it is inhaled, melted during use and released several chemicals including the toxicant formaldehyde cyanohydrin. The Environmental Protection Agency has listed formaldehyde cyanohydrin as “extremely toxic” and warned that inhalation of this chemical may cause asphyxiation, similar to that caused by hydrogen cyanide.

This research by Davis et. al. demonstrates the need for independent research on this and other ENDS products.  In particular, these iQOS products need further independent study since harmful chemicals can be released at the temperatures reached during pyrolysis.  

*Phillip Morris International does not define iQOS on their website.