Radiation pathology is the study of how radiation affects living tissues, including its effects on human health. Radiation can have both beneficial and harmful effects, depending on the dose and the type of radiation. Radiation is the emission of energy in the form of electromagnetic waves or particles. It can be found in nature or can be man-made. Natural sources of radiation include cosmic rays, radioactive elements in the earth's crust, and radiation from the sun. Man-made sources of radiation include medical diagnostic procedures, nuclear power plants, and nuclear weapons. When ionizing radiation enters living tissues, it can damage cells by breaking chemical bonds in DNA, proteins, and other molecules. This can lead to cell death or mutations that can cause cancer. The extent of the damage depends on the type of radiation, the dose, and the sensitivity of the tissue. The effects of radiation on living tissues are classified into two categories: deterministic and stochastic effects. Deterministic effects occur at high doses and have a predictable threshold level. Examples of deterministic effects include skin burns, radiation sickness, and cataracts. Stochastic effects occur at low doses and have no threshold level. Examples of stochastic effects include cancer and genetic mutations. In addition, radiation pathology is also used in diagnostic procedures, such as X-rays, CT scans, and PET scans. These procedures use low doses of ionizing radiation to create images of internal organs and tissues. Radiation pathology helps to ensure that the diagnostic benefits outweigh the potential risks of radiation exposure.