Physics: UV: the border case
Self-tutoring about radiation: the tutor mentions UV in terms of ionizing.
I mention ionizing vs non-ionizing radiation back in my post from Nov 10. The basic concept is that ionizing radiation can damage molecules in the body without your feeling it, while non-ionizing can’t. Therefore, ionizing is much more dangerous. X-rays and gamma rays are examples, but significant exposure to them doesn’t occur naturally.
The main type of radiation you hear people warn against, in everyday contexts, seems to be UV. UV is an interesting case: it’s ionizing, but can’t penetrate past the skin. In the skin and eyes, however, it can cause molecular damage. Hence the precautions surrounding it.
Source:
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.