This is the most detailed coverage I've seen so far.
ETA: Here's the abstract:
Here's what I think happened:
Some scientists heard that caffeine fights abnormal cell growth.
They got some specially bred hairless mice that are prone to squammous cell cancers and keratoacanthomas but NOT melanomas.
They put them in UV to simulate a lifetime dose of sunbathing in 20 weeks.
The mice got some suspicious growths.
Now, the scientists needed a (neutral) way to apply the caffeine, so they tried a moisturizer vs. plain water for 17 weeks (IIRC).
Surprise! The moisturizered mice got more cancer than the plain-water mice. Hmmm.
So they tried three more kinds of moisturizer. Same deal.
Then they called J&J and said, make us something like these 4 moisturizers but WITHOUT the sodium laureth sulfate (and mineral oil). J&J did. They reran the test with the new gunk. No extra tumors.
Scientists say, screw that whole caffeine thing; who gives a crap about that. Let's publish what we've got, but, to make sure we don't piss off people (like J&J) who supply us, we'll add a little boilerplate saying, this is too soon to conclude that moisturizers cause skin cancer. After all, these are _mice_.
Make of it what you will. I can't _wait_ to hear what the Environmental Working Group does with this puppy. As for the women-would-have-more-skin-cancer-than-men-if-this-were-real theory, it is to laugh.
ETA: EWG has been warning about a carcinogenic contaminant 1,4-dioxane of sodium laureth sulfate for a while. I do kinda wonder if this whole caffeine thing is a smoke screen for a direct assault on GRAS status for sodium laureth sulfate.
EWG on sodium laureth sulfate: