Introduction
Occupational lung diseases are caused by harmful particles, mists, vapors, or gases that are inhaled, usually while a person works. If the lung disease is due to inhaled particles, the term pneumoconiosis is often used. Where in the airways or lungs an inhaled substance ends up and what type of lung disease develops depend on the size and kind of particles inhaled. Large particles may get trapped in the nose or large airways, but very small ones may reach the lungs. There, some particles dissolve and may be absorbed into the bloodstream; most solid particles that do not dissolve are removed by the body's defenses.
The body has several means of getting rid of inhaled particles. In the airways, an accumulation of secretions (mucus) coats particles so that they can be coughed up more easily. Additionally, tiny cells lining the airways (cilia) are able to brush inhaled particles upward, out of the lungs. In the small air sacs of the lungs (alveoli), special scavenger cells (macrophages) engulf most particles and render them harmless.
Many different kinds of particles can harm the lungs. Some are organic, meaning that they are made of materials that contain carbon and are parts of the building blocks of living organisms (such as grain dusts, cotton dust, or animal dander). Some are inorganic, meaning that they are usually salts of metals (such as asbestos).
Different types of particles produce different reactions in the body. Some particles--animal dander, for example--can cause allergic reactions, such as hay fever-like symptoms or a type of asthma. Other particles cause harm not by triggering allergic reactions but by being toxic to the cells of the airways and air sacs in the lung. Some particles, such as quartz dust and asbestos, may cause chronic irritation that can lead to scarring of lung tissue (pulmonary fibrosis (see Section 4, Chapter 50)). Certain toxic particles, such as asbestos, can cause lung cancer, especially in smokers, or cancer of the lining of the chest and lung (mesothelioma), regardless of the person's smoking history.
 See the sidebar Who Is at Risk for Occupational Lung Diseases?
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