This post is a quick summary of the increasing risk of cancer with exposure to radiation. To my mind, there are two levels of risk: proven and unproven. Scientists have information on cancer risk from the great harm done by the nuclear bombs used during World War 2 as well as from the radiation exposure of a large population at Chernobyl. And enough years have passed since both events to evaluate the long term risk.
At this point, we know that an exposure of about 100 to 200 mSv (10 to 20 rems) raises your risk of cancer by a small amount, less than 1% increase over the background level (the usual number of cancer cases). As the radiation exposure goes higher, the risk of cancer goes up even more. But below 100 mSv (10 rems) of exposure, there is no statistically-verifiable increase in cancer risk. This is perhaps due to the rather high number of cancer cases in patients with no significant radiation exposure. In any case, there is no proven increase in cancer risk below 100 mSv (10 rems).
However, many scientists and researchers believe that any level of exposure to radiation increases your risk of cancer by at least a small amount. Below 100 mSv (10 rems), this theoretical increase in risk is small. The Nuclear Regulatory Commission (NRC) has this to say on the subject:
Although radiation may cause cancers at high doses and high dose rates, currently there are no data to establish unequivocally the occurrence of cancer following exposure to low doses and dose rates – below about 10,000 mrem (100 mSv). Even so, the radiation protection community conservatively assumes that any amount of radiation may pose some risk for causing cancer and hereditary effect, and that the risk is higher for higher radiation exposures. A linear, no-threshold (LNT) dose response relationship is used to describe the relationship between radiation dose and the occurrence of cancer. This dose-response hypothesis suggests that any increase in dose, no matter how small, results in an incremental increase in risk. The LNT hypothesis is accepted by the NRC as a conservative model for determining radiation dose standards, recognizing that the model may over estimate radiation risk. (NRC fact sheet)
And here’s the run-down on the increased risk with increased exposure to radiation:
100 to 200 mSv (10 to 20 rem)
0.7% increase in risk of solid cancers (tumors)
200 to 500 mSv (20 to 50 rem)
0.24% increase in risk of leukemia
1.55% increase in risk of solid cancers
500 to 1,000 mSv (50 to 100 rem)
0.46% increase in risk of leukemia
3.40% increase in risk of solid cancers
1000 to 2000 Sv (100 to 200 rem)
1.20% increase in risk of leukemia
6.40% increase in risk of solid cancers
greater than 2000 (200 rem) — if you survive:
3.10% increase in risk of leukemia
9.00% increase in risk of solid cancers
However, some researchers doubt the Linear No-Threshold model. Your body has some ability to repair damage to DNA from radiation, and so a very low dose, below 100 mSv, might not present much risk of cancer. See the PDF article: The safety of nuclear radiation for info on the risk and on the theory that very low doses might not present much risk.