question: radiation, why is it so bad for humans?
comment: Radiation can cause a random mutation in a cell that in turn could cause a cancer to develop, increase the amount of radiation and you increase the chances of this happening and becoming lethal.
passages: The health threat depends on the flux, energy spectrum, and nuclear composition of the radiation. The flux and energy spectrum depend on a variety of factors: short-term solar weather, long-term trends (such as an apparent increase since the 1950s), and position in the Sun's magnetic field. These factors are incompletely understood.
  
  The Mars Radiation Environment Experiment (MARIE) was launched in 2001 in order to collect more data.
   The Earth and all living things on it are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from protons to iron and larger nuclei derived from outside the Solar System. This radiation interacts with atoms in the atmosphere to create an air shower of secondary radiation, including X-rays, muons, protons, alpha particles, pions, electrons, and neutrons. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the geomagnetic field and altitude. For example, the city of Denver in the United States (at 1650 meters elevation) receives a cosmic ray dose roughly twice that of a location at sea level. This radiation is much more intense in the upper troposphere, around 10 km altitude, and is thus of particular concern for airline crews and frequent passengers, who spend many hours per year in this environment. During their flights airline crews typically get an additional occupational dose between per year and 2.19 mSv/year, according to various studies.
   Part of the uncertainty is that the effect of human exposure to galactic cosmic rays is poorly known in quantitative terms. The NASA Space Radiation Laboratory is currently studying the effects of radiation in living organisms as well as protective shielding.
  
  Section::::Prevention.:Drugs.
  
  Another line of research is the development of drugs that enhance the body's natural capacity to repair damage caused by radiation. Some of the drugs that are being considered are retinoids, which are vitamins with antioxidant properties, and molecules that retard cell division, giving the body time to fix damage before harmful mutations can be duplicated.
   Section::::Other sources of dose uptake.
  
  Section::::Other sources of dose uptake.:Medical.
  
  The global average human exposure to artificial radiation is 0.6 mSv/a, primarily from medical imaging. This medical component can range much higher, with an average of 3 mSv per year across the USA population. Other human contributors include smoking, air travel, radioactive building materials, historical nuclear weapons testing, nuclear power accidents and nuclear industry operation.
   Life on the Earth's surface is protected from galactic cosmic rays by a number of factors:
   Caution must be used in interpreting these results, as it noted in the BEIR VII report, these pre-doses can also increase cancer risk:
  
  However, 75 mGy/d cannot be accurately described as a low dose rate – it is equivalent to over 27 sieverts per year. The same study on dogs showed no increase in cancer nor reduction in life expectancy for dogs irradiated at 3 mGy/d.
  
  Section::::Studies of low level radiation.:Humans.
  
  Section::::Studies of low level radiation.:Humans.:Effects of sunlight exposure.
   BULLET::::- As already mentioned, radiation can have a toxic effect on organisms.
  
  Section::::Measuring.
   Section::::Science.
  
  Since astronauts are spending more time in outer space, they are receiving more exposure to ionizing radiation, a stream of particles that, when passing through a body, has enough energy to cause the atoms and molecules within that substance to become an ion. By directly or indirectly ionizing and thus damaging the components of living cells, including genetic material called DNA, ionizing radiation may cause changes in cells' ability to carry out repair and reproduction. This may lead to mutations, which, in turn, may result in tumors, cancer, genetic defects in offspring, or death.
   Part of the ISS year long mission is to determine the health impacts of cosmic ray exposure over the course of one year spent aboard the International Space Station.
   BULLET::::- Rothmund–Thomson syndrome (i.e. autosomal recessive association of congenital bone defects, hair and skin dysplasias, hypogonadism, and cataracts) is associated with increased risk of this disease.
  
  BULLET::::- Large doses of Sr-90 emission from nuclear reactor, nicknamed bone seeker increases the risk of bone cancer and leukemia in animals, and is presumed to do so in people.
   Radioactive materials produce ionizing radiation which may be very harmful to living organisms. Damage from even a short exposure to radioactivity may have long term adverse health consequences.
   Epidemiological studies are underway to identify health effects associated with the high radiation levels in Ramsar. It is much too early to draw unambiguous statistically significant conclusions. While so far support for beneficial effects of chronic radiation (like longer lifespan) has been observed in few places only, a protective and adaptive effect is suggested by at least one study whose authors nonetheless caution that data from Ramsar are not yet sufficiently strong to relax existing regulatory dose limits. However, the recent statistical analyses discussed that there is no correlation between the risk of negative health effects and elevated level of natural background radiation.
   At sufficiently high flux levels, various bands of electromagnetic radiation have been found to cause deleterious health effects in people. Electromagnetic radiation can be classified into two types: ionizing radiation and non-ionizing radiation, based on the capability of a single photon with more than 10 eV energy to ionize oxygen or break chemical bonds. Extreme ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing, and these pose their own special hazards: see "radiation" and "radiation poisoning". The last quarter of the twentieth century saw a dramatic increase in the number of devices emitting non-ionizing radiation in all segments of society, which resulted in an elevation of health concerns by researchers and clinicians, and an associated interest in government regulation for safety purposes. In the United States, this has resulted in legislation such as the Radiation Control for Health and Safety Act of 1968 and the Occupational Safety and Health Act of 1970. By far the most common health hazard of radiation is sunburn, which causes over one million new skin cancers annually in United States.
   Spacecraft, both manned and unmanned, must cope with the high radiation environment of outerspace. Radiation emitted by the Sun and other galactic sources, and trapped in radiation "belts" is more dangerous and hundreds of times more intense than radiation sources such as medical X-rays or normal cosmic radiation usually experienced on Earth. When the intensely ionizing particles found in space strike human tissue, it can result in cell damage and may eventually lead to cancer.
   Section::::Early radiation dangers.
   Section::::Human health effects.
   However, some studies contradict the linear no-threshold model. These studies indicate that some low levels of radiation do not increase cancer risk at all and that there may exist a threshold dosage of ionizing radiation below which exposure should be considered safe. Nonetheless, the 'no safe amount' assumption is the basis of US and most national regulatory policies regarding "man-made" sources of radiation.
  
  Section::::Cause.
   High radiation doses can cause DNA damage. If left unrepaired, this damage can create serious and even lethal chromosomal aberrations. Ionizing radiation can produce reactive oxygen species, which are very damaging to DNA.
   Of the above factors, all but the first one apply to low Earth orbit craft, such as the Space Shuttle and the International Space Station. Exposures on the ISS average 150 mSv per year, although frequent crew rotations minimize individual risk. Astronauts on Apollo and Skylab missions received on average 1.2 mSv/day and 1.4 mSv/day respectively. Since the durations of the Apollo and Skylab missions were days and months, respectively, rather than years, the doses involved were smaller than would be expected on future long-term missions such as to a near-Earth asteroid or to Mars (unless far more shielding could be provided).
   On 31 December 2012, a NASA-supported study reported that manned spaceflight may harm the brains of astronauts and accelerate the onset of Alzheimer's disease. This research is problematic due to many factors, inclusive of the intensity of which mice were exposed to radiation which far exceeds normal mission rates.
   In accordance with ICRP recommendations, most regulators permit nuclear energy workers to receive up to 20 times more radiation dose than is permitted for the general public. Higher doses are usually permitted when responding to an emergency. The majority of workers are routinely kept well within regulatory limits, while a few essential technicians will routinely approach their maximum each year. Accidental overexposures beyond regulatory limits happen globally several times a year. Astronauts on long missions are at higher risk of cancer, see cancer and spaceflight.
   On Earth, in developed nations, humans are exposed to about 0.6 rads per year, and aboard the International Space Station about 8 rads per year. Humans can tolerate up to about 200 rads of radiation without incurring permanent damage, however any radiation exposure carries risk so there is a focus on keeping exposure as low as possible. On the surface of Mars there are two main types of radiation: A steady dose from a variety of sources and solar proton events that can cause a dramatic increase in the amount of radiation for a short time. Solar flare events can cause a lethal dose to be delivered in hours if astronauts are caught unprotected, and this is a concern of NASA for human operations in space and on the surface of Mars. Mars does not have a large magnetic field in the same way as Earth, which shields the Earth from radiation, especially from solar flares. For example, the solar event which occurred on August 7, 1972 just 5 months after Apollo 16, produced so much radiation, including a wave of accelerated particles like protons, that NASA became concerned what would happen if such an event were to occur while astronauts were in space. If the astronauts get too much radiation, it increases their lifetime cancer risk and they can get radiation poisoning. Exposure to ionizing radiation can also cause cataracts, a problem with the eye.
   Natural radiation is found everywhere; it is in the air, water, soil, rocks, minerals and food. The largest amount of radiation comes from radon. Certain places are called 'high background radiation areas' (HBRAs), such as Guarapari, Southwest of France, Ramsar, parts of China, and Kerala Coast. People living in these areas however have not shown any health deficiencies and in some cases are even healthier and live longer than those not in HBRAs.
  
  Section::::Diseases.:Other Issues.
   Estimates are that humans unshielded in interplanetary space would receive annually roughly 400 to 900 mSv (compared to 2.4 mSv on Earth) and that a Mars mission (12 months in flight and 18 months on Mars) might expose shielded astronauts to roughly 500 to 1000 mSv. These doses approach the 1 to 4 Sv career limits advised by the National Council on Radiation Protection and Measurements (NCRP) for low Earth orbit activities in 1989, and the more recent NCRP recommendations of 0.5 to 2 Sv in 2000 based on updated information on dose to risk conversion factors. Dose limits depend on age at exposure and sex due to difference in susceptibility with age, the added risks of breast and ovarian cancers to women, and the variability of cancer risks such as lung cancer between men and women.
   The ICRP recommends, develops and maintains the International System of Radiological Protection, based on evaluation of the large body of scientific studies available to equate risk to received dose levels. The system's health objectives are "to manage and control exposures to ionising radiation so that deterministic effects are prevented, and the risks of stochastic effects are reduced to the extent reasonably achievable".
  