Soot is produced after the incomplete burning of organic material like wood or coal. It was first described as a carcinogen 250 years ago when a London surgeon, Sir Percival Pott, associated increased incidence of scrotal cancer in (often young male) chimney sweeps. This is considered the first documented medical case of occupational cancer in the world. Polyaromatic hydrocarbons (PAHs) are considered one of the main groups of carcinogens in soot. Let's hope that Santa has modernised his present-delivery system to circumvent chimneys.