Body chemistry? *puts some ph paper on tongue*
Im guessing you mean sweat and grease build-up over time.
I wipe my strings down every time I play/practice. I guess the life-span of certain strings is,
to some extent, down to the production process.
Obviously flatwounds will last longest given the types of tone they give out.
There are lots of brands out there and maybe there is a perfect match out there for me somewhere.