Ah ha, boboboy, which is better: for the sun's UV to break up the molecules on the layer of creme that is on the outside of your skin, or for the sun to break up the molecules in your skin? The sunscreen has some reflective properties, but it also is there to be sacrificial so that the molecules on the sunscreen get broken up rather than the ones of your skin. Those molecules on the outside adsorb the rays, and the reaction of those molecules are just like I've been saying. This is a large reason why sunscreen needs to be reapplied periodically (that and a lot of them get wiped off with sweat).
Please go read an organic chemistry textbook, or even better a textbook on polymerization, especially the chapters about how organic molecules react to UV radiation. Again, in polymerization all the time, UV lamps are used to keep the reactions going. The reactions keep going because the UV radiation energizes the molecules, and the molecules use this extra energy to bond together. This (
http/www.emeraldinsight.com/fig/1560060101001.png ) isn't the best picture, but it is an example of what I am talking about. The organic molecules on the left are very stable just on their own. But, being exposed to UV light breaks open those double bonds, and the moleucules start to bond together to fulfill the bonding requirements. UV light can also break open rings and sometimes single bonds. And so, UV can break open the bonds of the chemicals in the tea tree oil, and make them bond with other things, or polymerize together or who knows. If UV light didn't do this, why would they be used all the the time in polymerization experiments and even on the processing level? For that matter, some printers have a UV lamp in them so that the ink bonds together and hardens rather than runs. It is very well understood the way UV light reacts with organic molecules. And you don't have to take my word for it, go to your library and read a book on organic chemistry or polymerization.
I told you before, I couldn't find any study on what specifically happens to the ingredients in tea tree oil when exposed to UV. Most likely, there isn't a big call for that knowledge in the research world. It just hasn't been studied because it isn't all that interesting. And, it isn't all that interesting because it has been known for a long time what happens to organic chemicals when exposed to UV. But, again, if you look these things up in the proper texts, not just on the Internet, you will find it is pretty well understood. Just because no one has done a study on it does not mean that it doesn't occur. I am trying to share my expertise and knowledge about such things, I have studied them and read journal articles about polymerization using UV, if you are really going to be stubborn I'll dig out my organic chemistry book and my polymers book but I'd rather not since I plan on moving soon and they are packed away. But, like I said, any good polymers book or organic chemistry book is going to talk about the reaction organic chemicals have to UV light. Again, you don;t just have to take me word for it, this can be independently checked by you. Please do go check these out on your own before you try to argue these points again, because if you don't, it is only an argument of your beliefs versus the facts I am trying to present. And it seems right now no matter how many facts I try to present you are just going to believe what you are going to believe, and it is pointless for me to continue. I'd personally rather continue to try to discuss these issues and others scientifically and share my knowledge of chemical processes, but if I have to argue against just belief and not fact, it is pointless to try to continue. Please let me know how you want to proceed.