Why do old books smell different from new ones?

The smell of an old book comes from chemical changes in its materials. Paper made from wood contains lignin and cellulose, and as lignin breaks down it releases aromatic compounds, including vanillin-like scents. Adhesives, inks, and paper coatings can also age and emit their own volatile organic compounds. Humidity, heat, and storage conditions affect how strong the smell becomes. Librarians and conservators can even use the scent and condition of paper as clues about a book’s age and preservation state.