The term "trace evidence" is generally thought of as any type of evidence occurring in sizes so small that it can be transferred or exchanged between two surfaces without being noticed.
Fiber and textile evidence can provide strong evidence of an association in criminal cases. The individual microscopic fibers that comprise the variety of textile materials in the world can be transferred from person to person and place to place, indicating what environment someone has been in. These fibers are compared to suspected sources of origin in the South Dakota Forensic Laboratory using a protocol including stereo, brightfield, polarized light, fluorescence and comparison microscopy, Fourier transform infrared microscopy (FTIR) and microspectrophotometry.
Examination can reveal whether the hair is animal or human. If the hair is of human origin, the race of the donor and the area of the body from which it originated can be determined. Microscopical examination can also determine if the hair was cut, pulled, naturally shed, if it originated from a living or dead person, if the hair has been subjected to artificial treatments such as bleaching, coloring, or permanent waves. Damage due to disease or exposure to fire can also be detected. All this information can be important to the investigators when they know nothing about the perpetrator of a crime.