Diseases not known to be caused by infectious agents include the three leading killers in the United States and other developed countries: heart disease, most cancers, and cerebrovascular disease (decreased blood circulation in the brain). Noninfectious illnesses include disorders as terrifying as Alzheimer's disease, which robs victims of their memory and their ability to reason, and as pesky as poison ivy.
Degenerative disorders, including arthritis, Parkinson disease, and Alzheimer's disease, involve the progressive breakdown of tissues and loss of function of parts of the body. Joints gradually become stiff; bones become brittle; blood vessels become blocked by deposits of fat. The incidence of these problems increases with age , and, in at least some cases, progression can be slowed by good health habits.
Environmental factors play critical roles in numerous noninfectious diseases. Exposure to carbon monoxide can have long-term effects on the heart and vision. Lead in drinking water can impair children's mental abilities and increase blood pressure in adults. Occupational exposure to coal dust, cotton dust, and asbestos predisposes workers to black lung, brown lung, asbestosis, and other respiratory diseases (Occupational and Environmental Diseases). Other diseases are caused by an addiction to a harmful substance. Tobacco smoking is a prime culprit in emphysema, as well as lung cancer and other respiratory diseases. Excessive use of alcohol can lead to liver disease, brain damage, and nutritional disorders.
Repetitive stress injuries result from repeating certain motions, usually from a fixed or awkward posture. Twisting items on a factory assembly line, carrying bulging mailbags, using vibrating tools such as pneumatic hammers, or practicing the piano or a tennis stroke for hours on end can all result in pain, inflammation, and permanent nerve damage.