Another commentator said that the studies were done on animals, not people.

I wish they would do a study to determine whether cancer rates are higher/lower
for people who wash their hands frequently, especially before eating, going to
the bathroom, touching their own or someone else's breasts, skin, faces,
genitals, mouth, etc. etc.  

Smoke residue sticks to surfaces and it is possible that all those lab animals
got their cancers by touching lab surfaces and then licking their paws and other
body parts.  

Ora