Fiberglass insulation or glass wool is a man-made vitreous fiber. It is made by pulling strands of glass into thin fibers. People can be affected by fiberglass when they come into contact with it either during the manufacturing process or when it is being used in a building. Construction workers who install or remove insulation often come into contact with fiberglass. Homeowners can also come across fiberglass insulation during repairing or clearing out the attic. If the insulation is not properly sealed off it can get into air vents and circulate through the building. Fiberglass insulation is not generally considered to be dangerous, but it can irritate the skin and respiratory system.
When bare skin comes into contact with fiberglass the sharp ends of the strands can cause irritation through scratching, creating tiny cuts. This will only be a temporary effect, but it can be uncomfortable. This effect is known as mechanical irritation because the fiberglass does not react with the skin, it just rubs against it. The Occupational Safety and Health Administration does not therefore class fiberglass as an irritant, as this term is restricted to substances which cause chemical reactions.
Fiberglass releases tiny fibers and particles into the air when it is disturbed. Many of these are small enough to be breathed in by anyone nearby. Strands of fiberglass which enter the respiratory system can cause irritation in exactly the same way as they do when they touch the skin. The nose, throat and lungs can all be affected, although, as with the skin, the irritation will be temporary. There is no evidence of any long term damage, and workers who come into regular contact with fiberglass insulation are not at any higher risk of lung and breathing problems.
The National Toxicology Program's 11th "Report on Carcinogens" lists glass fibers under the category "reasonably anticipated to be a human carcinogen". This implies that there is some evidence of fiberglass causing cancer, but no definite proof of an effect in humans.
A 1988 report from the International Agency for Research on Cancer (IARC) provided the main evidence for a possible link between fiberglass and cancer in animals. When this report was updated in 2002, it found there was inadequate evidence of fiberglass insulation causing cancer in humans, and only limited evidence of any effect in animals.