Smell is chemistry, and the chemistry of old books gives your cherished tomes their scent. As a book ages, the chemical compounds used—the glue, the paper, the ink–begin to break down. And, as they do, they release volatile compounds—the source of the smell. A common smell of old books, says the International League for Antiquarian Booksellers, is a hint of vanilla: “Lignin, which is present in all wood-based paper, is closely related to vanillin. As it breaks down, the lignin grants old books that faint vanilla scent.”

via That “Old Book Smell” Is a Mix of Grass and Vanilla | Smart News.