What substance can cause cotton to stain more easily than synthetic fibers?

Cotton is a natural fiber that is more absorbent than synthetic fibers. When exposed to water, cotton fibers can easily take up moisture and any dissolved substances that might be present in the water, leading to potential staining. Unlike synthetic fibers, which are often treated to be water-resistant or hydrophobic, cotton allows liquids to penetrate quickly, making it more susceptible to staining from contaminants that might be carried in with the water.

In contrast, oils tend to affect both cotton and synthetic fibers, but cotton's absorbent nature may lead to a more significant impact when it comes to water-based stains. Heat can indeed exacerbate staining by setting stains or causing fibers to take up dyes, but it doesn’t directly cause staining itself. Solvents are used in cleaning processes but can sometimes damage fibers if not used properly, rather than being a direct cause of staining. Thus, water is the primary substance that causes cotton to stain more easily due to its absorbency and inherent characteristics.