system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 How do bookstores prevent book pages from turning yellow?
gpt
Technically, they don't prevent it.  There are at least two reasons why you don't SEE the pages turning yellow on the bookshelves in a bookstore:

1. Books don't stay on their shelves long enough for you to notice the pages yellowing.
2. Their A/C works to keep the humidity LOW.  Keeping the air dry slows the aging process of paper.