One interesting result from the Ames test is that the dose response curve using varying concentrations of the chemical is almost always linear, indicating that there is no threshold concentration for mutagenesis. It therefore suggests that, as with radiation, there may be no safe threshold for chemical mutagens or carcinogens. However, some have proposed that organisms could tolerate low levels of mutagens due to protective mechanisms such as DNA repair, and thus a threshold may exist for certain chemical mutagens. Bruce Ames himself argued against linear dose-response extrapolation from the high dose used in carcinogenesis tests in animal systems to the lower dose of chemicals normally encountered in human exposure, as the results may be false positives due to mitogenic response caused by the artificially high dose of chemicals used in such tests. He also cautioned against the "hysteria over tiny traces of chemicals that may or may not cause cancer", that "completely drives out the major risks you should be aware of".