Newspapers turn yellow over time due to a process called *lignin oxidation*. Lignin is a polymer that is found in the cell walls of plants, and it is what gives paper its strength and rigidity. Lignin is also susceptible to oxidation, which is a chemical reaction that involves the loss of electrons. When lignin is oxidized, it produces a yellow pigment called *lignin chromophore*. The longer a newspaper is exposed to air and light, the more the lignin in the paper will oxidize, and the yellower the paper will become.

In addition to lignin oxidation, other factors can also contribute to the yellowing of newspapers, including:

* Acidity: Acidic conditions can accelerate the oxidation of lignin. This is why newspapers that are stored in acidic environments, such as libraries or archives, yellow more quickly than newspapers that are stored in neutral or alkaline environments.

* Heat: Heat can also accelerate the oxidation of lignin. This is why newspapers that are exposed to high temperatures, such as those that are stored in attics or garages, yellow more quickly than newspapers that are stored in cool environments.

* Light: Light can also contribute to the yellowing of newspapers. This is why newspapers that are exposed to direct sunlight, such as those that are displayed on newsstands, yellow more quickly than newspapers that are stored in dark environments.

By understanding the factors that contribute to the yellowing of newspapers, you can take steps to protect your newspapers from yellowing and keep them looking their best for as long as possible.