The 1 mSv/Y guideline is based on a hypothesis that extrapolating downward from higher dosages that have well understood health effects we can infer the effects

The 1 mSv/Y guideline is based on a hypothesis that extrapolating downward from higher dosages that have well understood health effects we can infer the effects of lower dosages. They call this the Linear no-threshold model. It was chosen because it's the most conservative, safest option. Scientists suspect that it's wrong though. We have DNA repair mechanisms that may catch many errors. The wikipedia article (http://en.wikipedia.org/wiki/Linear_no-threshold_model http://en.wikipedia.org/wiki/Linear_no-threshold_model) is pretty good.