That tobacco smoke exposure of one generation may affect the next generation is provocative and plausible. Tobacco smoke is a complex mixture of toxicants, mutagens, and carcinogens, and there is ample evidence that it can have an impact on genes and gene expression. Rodent studies have shown that nicotine exposure of the parents from gestation through early life can alter DNA methylation patterns in their gonadal tissue, with different effects on testes vs ovaries, and goes on to have an adverse impact on the lung function of second-generation offspring, even when the offspring had no nicotine exposure themselves.10 Studies of genetic material from newborns showed that in utero exposure is associated with altered DNA methylation patterns, with the degree of alteration proportional to the cord blood cotinine levels.11 DNA methylation patterns influence gene expression. Epigenetics refers heritable changes in gene activity that are not caused by changes in the DNA sequence. It is a mechanism where the environment can influence gene expression in a manner that can be passed down through generations. Epigenetic mechanisms have been postulated to account for the impact of in utero tobacco smoke exposure on the development of asthma and allergies.12 Whether epigenetic changes are reversible is not known; however, because adverse impacts of in utero tobacco smoke exposure on disease can be detected many years later, it is likely that many of these changes persist.