Most adverse health effects of exposure to<unk>  may be grouped in two general categories: *deterministic effects (harmful tissue reactions) due in large part to killing or malfunction of cells following high doses from<unk>  burns. *stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells. The most common impact is stochastic induction of cancer with a latent period of years or decades after exposure. For example,<unk>  is one cause of chronic myelogenous leukemia, although most people with CML have not been exposed to<unk> . The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. The most widely accepted model the Linear no-threshold model (LNT) holds that the incidence of cancers due to<unk>  increases linearly with effective<unk>  dose at a rate of 5.5% per sievert. If this is correct, then natural background<unk>  is the most hazardous source of<unk>  to general public health, followed by medical imaging as a close second. Other stochastic effects of<unk>  are teratogenesis, cognitive decline, and heart disease. Although DNA is always susceptible to damage by<unk> , the DNA molecule may also be damaged by<unk>  with enough energy to excite certain molecular bonds to form pyrimidine dimers. This energy may be less than<unk> , but near to it. A good example is ultraviolet spectrum energy which begins at about 3.1 eV (400 nm) at close to the same energy level which can cause sunburn to unprotected skin, as a result of photoreactions in collagen and (in the UV-B range) also damage in DNA (for example, pyrimidine dimers). Thus, the mid and lower ultraviolet electromagnetic spectrum is damaging to biological tissues as a result of electronic excitation in molecules which falls short of ionization, but produces similar non-thermal effects. To some extent, visible light and also ultraviolet A (UVA) which is closest to visible energies, have been proven to result in formation of reactive oxygen species in skin, which cause indirect damage since these are electronically excited molecules which can inflict reactive damage, although they do not cause sunburn (erythema). Like ionization-damage, all these effects in skin are beyond those produced by simple thermal effects.
Ionizing radiation
Irradiation
Radiation
Co-carcinogen
Immunologic adjuvant
Food irradiation
Carcinogen
Radiosensitizer