Polycyclic aromatic hydrocarbons back to 'Safer' Cigarettes: A History This animation shows how the heat from tobacco combustion causes molecules to fragment into unstable arrangements, which recombine to form carcinogenic compounds of polycyclic aromatic hydrocarbons, or PAH's. Anatomy of a Cigarette | "Safer" Cigarettes: A History | The Dope on Nicotine On Fire | Resources | Transcript | Site Map | Search for a Safe Cigarette Home Search | Site Map | Previously Featured | Schedule | Feedback | Teachers | Shop Editor's Picks | Join Us/E-Mail | About NOVA | Watch NOVAs online | To print PBS Online | NOVA Online | WGBH © | Updated August 2001