Why does paper yellow?

According to the definition, wood-free picture paper contains a maximum of 5% wood-containing pulp. Wood-containing paper contains at least 5% wood-containing pulp by weight. Wood-containing papers include LWC (Light Weight Coated) papers or newsprint. The proportion of wood-containing pulp has a significant influence on the yellowing of the paper.

Book with yellowing pages
© Photo by Katrina S on Pixabay
09.05.2022

Why does wood-containing paper yellow?
Yellowing is caused by a substance called lignin. Wood-containing paper contains a lot of lignin. If the wood-containing paper is now exposed to daylight (UV-containing sunlight), the lignin contained reacts with a photochemical reaction and turns yellow.

Newsprint yellows particularly quickly
Newspapers produced on newsprint - i.e. paper containing wood - can show a yellow discoloration after just a few days unprotected in direct sunlight. Even storage inside a room where even a little daylight can penetrate is enough to cause the newspapers to yellow.