Why do books get moldy after being kept for a long time?

Generally speaking, paper turns yellow because of oxidation. If we can avoid oxidation as much as possible, we can also avoid yellowing of the paper. As long as you can guarantee the following three points, paper yellowing can basically be avoided. These three points are to reduce contact with air, water and sunlight. For most people, contact with air is inevitable, but contact with moisture and sunlight can be avoided as much as possible. If you don't use some books often, you can try to seal them in a plastic bag and take them out when you use them. Usually, the shelf life of paper should not exceed one year. Even if the storage conditions of paper are good, the paper will change color and deteriorate if it is stored for too long. If the paper is stored for two years, the coated paper will turn yellow and lose powder; Newsprint turns yellow and brittle; The wrapping paper is discolored and its strength is reduced; Yellow paperboard and box paperboard will go moldy and deteriorate, and so on.