Human Body Organs Kidneys

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Health is a difficult state to define, but relates to the self-defined perception of an individual and includes physical, mental, social and cultural factors. [citation needed] The absence or deficit of health is illness which includes disease and injury. Diseases cause symptoms felt, seen or perceived by a person, and signs which may be visible on a medical examination. Illnesses may be from birth (congenital) or arise later in life (acquired). Acquired diseases may be contagious, caused or provoked by lifestyle factors such as smoking, alcohol use and diet, arise as the result of injury or trauma, or have a number of different mechanisms or provoking factors. As life expectancy increases, many forms of cancer are becoming more common. Cancer refers to the uncontrolled proliferation of one or more cell types and occurs more commonly in some tissue types than others. Some forms of cancer have strong or known risk factors, whereas others may arise spontaneously. Depending on the type of cancer, risk factors can include exposure to carcinogens and radiation, excessive alcohol or tobacco intake, age, and hormone imbalances in the body.