Hair resists the decomposition process, and different types of hair have different degrees of resistance. Hair has an exterior cuticle composed of scales that overlap and protect the hair from the normal mechanisms that lead to decomposition, according to the U.S. Department of Energy.
Decomposition is the process of tissue breaking down after a plant or animal has died. Within 72 hours after death, some tissues begin to decay and bacteria start feeding on the dead tissue. In turn, the bacteria release gas that makes the tissues bloat, pushing fluids out and drawing flies and maggots in, according to Forbes. However, the cuticle around the hair protects it from this bacterial invasion, which is why hair from historical figures such as Copernicus and George Washington is still in museums.