I still can't get over your statement, boboboy, how are the products found in nature not chemicals?
Perhaps it is a difference in terminology here, but to me, everything is a chemical. Including the long carbon and oxygen chains of molecules that make up tea tree oil. There is no one ingredient in tea tree oil. It is a mix of many different hydrocarbons. But, look at
http/en.wikipedia.org/wiki/Sabinene the entry on one of the ingredients. UV light has the ability to break that double bond, which allows Sabinene to bond something else. Maybe another double-bond-broken Sabinene, maybe another ingredient in the oil that is also reactive from exposure to UV, who knows. The point is, it will go off and form another compound that is NOT naturally occuring in the oil. This is what you probably don't want exposure to. Look, I don't know exactly what will happen, what byproducts will be produced. At the very least, the molecules that have been changed will not be there to do the job they are supposed to do.
I have not performed the experiment and I can't find any report by anyone who has. But, I do know what the normal reaction large, organic molecules do have when exposed to UV light. That is what I am basing my guesses on.
Finally, can I ask where you are basing your knowledge that UV has no adverse affect on melafix from? I'll tell you mine: several semesters of studying organic chemistry and polymers while earning my graduate degree. If you open any decent organic chemistry book, you can learn how UV attacks the bonds in organic chemicals. How can you say so confidently that it doesn't? Especially in the face of all the scientific evidence that it does?