Why can't our body resist radiation?

Our body construction and components (Cells, bones, even the blood) is already resisting radiation. What I mean is that every day, we are exposed to radiation, so our body does resist radiation, but all has a limit, so if we overcome that limit, we might suffer deep injuries and even death.

In resume, we do resist radiation, but no high level exposition.

because effects of radiation include nausea, hair loss, and dry mouth. other side effects include muscle soreness, dry skin, and fatigue #believe