If inhaled, . Some inhaled fibers are trapped by the mucous in the breathing passageways or in nasal hair. The body expels a large percentage of these trapped fibers. However, since many of the asbestos fibers in the air are smaller than 1/1000 the size of a human hair, these extremely small fibers escape the body's initial defense systems and can penetrate deep into the lungs. A human inhaling these small fibers usually will not experience any immediate symptoms, such as sneezing or itching. These fibers, which lodge deep in the lungs, can remain there for years before any symptoms of disease begin to appear. Many of the World War II shipyard workers exposed to asbestos did not manifest any disease symptoms for after initial exposure.