I worked for a company that made tiki torch fuel. Nothing in this fuel was known to the state of CA as a cancer-causing compound and so we didn't need the Prop 65 warning.
A person in California was using it and noticed it produced some smoke...which as Hikemor mentions IS considered a carcinogen. They reported it to the CA state prop 65 bounty hunter authorities, and we ended up being fined nearly $100,00 because the USE of our product could cause cancer. This was a novel, legal interpretation of the word "contains".
-Blast