A genetic disease characterized by such extraordinary sensitivity to sunlight that it results in the development of skin cancer at a very early age.

Children with xeroderma pigmentosum can only play outdoors safely after nightfall. They have been called "midnight children", the "children of the dark", the "children of the night", and "vampire children".

Anyone with xeroderma pigmentosum develops severe sunburn and eye irritation within minutes of exposure to sunlight.

Other signs of XP include the development of ultradry skin (the word "xeroderma" means extreme dryness of the skin) plus blisters, heavy freckling, and dark spots on the skin (the word "pigmentosum" refers to these pigmented areas of the skin).