How many chemicals are in tobacco smoke?
It is often said that smoke contains over 4,000 chemicals (see example US-EPA). But what does this number actually mean? It may be that 4,000 have been identified in smoke, but numbers like this are easily misunderstood. How many chemicals are present depends on where one draws a line of relevance how much has to be present before the chemical is counted? Obviously the line could be drawn at the single molecule, in which case many more than 4,000 detected might be present – most undetectable with lab instruments. But the same applies to car exhausts, BBQs, garden bonfires and even to ambient fresh air. The number is not really meaningful in public health terms if it includes chemicals where there is only a single molecule present. The number of chemicals itself is not really important – what matters is the toxicity of the chemicals and how much of the toxic chemicals are present. Smoke would be more harmful with a smaller number of more harmful chemicals in greater concentrations.
