I have no scientific data to support it but I feel as if a lot of my pepper plants that I transplant do not grow as well as those that I have done when my hands are completely clean. Sometimes when I am taking starts out of the propagation chamber and transplanting them into 6 packs (sometimes 10-15 thousand starts at a time) I smoke during the work and other times I have a lighter load to do maybe 1500 to 2000 starts and I do not smoke during the transplant( shorter period of time working) and it seems that the small batches grow better(faster). I see no difference in any other vegetable or ornamentals that I grow. No affect on hanging baskets etc.