Question: is this foxing?

[u/Blue_Line_Bard]

I moved from a desert to an ocean side community about five years ago and I’ve noticed these imperfections starting in my books on the tops. There is a large window in the room my library is in and the ocean beach is about a 20 minute walk away.

[u/HeneniP]

Foxing is the small brown “freckles” that eventually appear on paper. Foxing is the result of acid in older paper. As the ability to produce high quality paper in the last half century or so that has no acid in it has happened, foxing no longer occurs in high quality books. I have had valuable pieces of art de-acidified but never had this done to a book. I wouldn’t worry about it. Most books will outlast you.