What are genetic and metabolic metabolic photosensitive dermatoses?

There are two main types of metabolic photosensitive dermatoses: pellagra, and porphyrias. There are other conditions too, including:

Xeroderma pigmentosum – an inherited disorder where DNA cannot be repaired properly (DNA can be damaged by exposure to UV light)
Bloom syndrome – an inherited disorder where our genetic material can break down and rearrange in the wrong order
Cockayne syndrome – another inherited disorder involving faulty repair of DNA. The brain and many other organs and systems can be affected in Cockayne disease