The generation of formaldehyde in cigarettes--Overview and recent experiments

In recent years much effort has been devoted to assessing the influence of tobacco ingredients on the chemistry and toxicity of cigarette mainstream smoke. All of the studies have indicated that commonly used tobacco ingredients do not change the toxicity of smoke as measured in specified assays. Also, the ingredients have little effect on the levels of most smoke constituents that may be relevant to smoking-related diseases. One exception to this generalisation is formaldehyde, which is generated from saccharides used as tobacco ingredients. However, the past studies have generally used mixtures of ingredients added to the tobacco so that the exact effect of each saccharide in turn could not be precisely determined. This is addressed in the present study. Many diverse studies over the last 30 years have examined particular aspects of formaldehyde in smoke and its generation although no attempt has been made to draw the various aspects together. This has also been addressed in the present paper and an overview is developed on the subject. The experimental results of the present study are rationalised within the framework of this previous knowledge. In the present experimental study, several individual saccharides commonly used as tobacco ingredients have been added to cigarettes, the cigarettes have been machine-smoked and the yields of formaldehyde in the resultant smoke have been compared to those from a control (no ingredient) cigarette. Using four series of cigarettes made on different occasions, the results indicate that all tested sugars added to tobacco increase the yield of formaldehyde in mainstream cigarette smoke under ISO standard smoking machine conditions. Increases up to 60% are observed at maximum sugar levels used on cigarettes. The increases are mostly statistically significant although their magnitudes are variable. These results with formaldehyde are consistent with all previously published studies on the subject. The increases in mainstream formaldehyde are also observed using smoking machine conditions that are more intense than the standard ISO conditions. Different sugars increase mainstream formaldehyde to different extents, which may be due at least partially to the presence of varying amounts of amino compounds in some of the sugars, such as honey and maple syrup. The presence of such compounds has been shown to inhibit the generation of formaldehyde from sugars. In general, the first puff of the cigarette generates abnormally high yields of formaldehyde, and this effect has been shown to persist in the presence of added sugars. In contrast to the situation with mainstream smoke, the levels of formaldehyde in sidestream smoke are not affected by the presence of sugars. The addition of the various saccharides to tobacco also produced some statistically significant effects in the cigarette mainstream yields of six other carbonyl smoke constituents that were analysed at the same time as formaldehyde. These effects were generally small, less than 16%, were not consistent amongst the various cigarette series and lost their significance when the long-term analytical variability was taken into account.