cigs vs rems
consider a graph of harm versus exposure. many substances have zero harm up to a safe dosage. then harm grows more less linearly. some substances have no safe dosage. that simply means the flat part is really short. cigarettes and radiation are two examples. are these things dangerous? well, it depends on how fast the linear part grows. for cigarettes it grows alarmingly fast. so yes, they are dangerous. radiation hazard grows far more slowly. so yeah, you want to limit your exposure. but occasional high doses are no big deal. as long as they're infrequent. like mammograms and ct scans. and oopses at nuclear power plants.