What causes permanent color loss in fabrics due to exposure?

Fading is a process where the color of a fabric gradually weakens and diminishes, often due to prolonged exposure to light, heat, or certain chemicals. This type of color loss is permanent because it alters the fabric on a chemical level, breaking down the dye molecules and causing them to lose their vibrancy. In many cases, fading is most pronounced in areas that receive direct sunlight, such as furniture near windows.

The other options, while they relate to issues with fabrics, do not specifically cause permanent color loss through exposure. Staining refers to the introduction of unwanted color or substance onto a fabric, which may be removable depending on the type of stain and the fabric's cleaning process. Crocking refers to the transfer of color from one fabric to another through rubbing or friction, rather than a loss of the original color. Discoloration can occur for various reasons, including staining or chemical reactions, but does not necessarily indicate the fading process that leads to permanent loss of color due to exposure. Thus, fading is the specific answer that directly addresses permanent color loss from exposure.