I live in Florida, and the humidity outside fluctuates between 60%-99% throughout the day. The RH % where my bookshelf is (in the closet) can fluctuate anywhere as low as 39% (unusual, usually only in cold weather) to 60%, and has sometimes been seen to get to around 65%. For the most part it's relatively stable around 58%-62%, but I'm wondering if this high humidity will damage my books eventually. My mass market paperbacks always seem to brown and yellow, but I guess that's natural. Do slip cases protect books from yellowing further? Also, how about temperature fluctuations due to your bookcase being up against an outer wall? I typically leave my closet door open to help circulate air, as well as having a dehumidifier hooked up in there.

Something interesting to note: I have never observed wavy pages in my books or anything of the sort even at 65% humidity in my house. I take a look at them often to see what's up, and the pages are always crisp and everything looking fine.

I just want to hear everyone's thoughts on this topic, and hear what you guys do to keep your books safe! For the record, my books are just on a faux-wood bookshelf. Almost all of them are in mylar protectors from brodart, save for the paperbacks obviously, which are usually in slipcases.