<Li> causes skin aging (but at a slower rate than UVA). </Li> <Li> stimulates the production of new melanin, which leads to an increase in the dark - coloured pigment within a few days . </Li> <P> A person's natural skin color affects their reaction to exposure to the sun . An individual's natural skin color can vary from a dark brown to a nearly colorless pigmentation, which may appear white . In 1975, Harvard dermatologist Thomas B. Fitzpatrick devised the Fitzpatrick scale which described the common tanning behavior of various skin types, as follows: </P> <Table> <Tr> <Th> Type </Th> <Th> Also called </Th> <Th> Sunburning </Th> <Th> Tanning behavior </Th> <Th> von Luschan scale </Th> </Tr> <Tr> <Td> </Td> <Td> Very light or pale </Td> <Td> Often </Td> <Td> Occasionally </Td> <Td> 1--5 </Td> </Tr> <Tr> <Td> II </Td> <Td> Light or light - skinned </Td> <Td> Usually </Td> <Td> Sometimes </Td> <Td> 6--10 </Td> </Tr> <Tr> <Td> III </Td> <Td> Light intermediate </Td> <Td> Rarely </Td> <Td> Usually </Td> <Td> 11--15 </Td> </Tr> <Tr> <Td> IV </Td> <Td> Dark intermediate </Td> <Td> Rarely </Td> <Td> Often </Td> <Td> 16--21 </Td> </Tr> <Tr> <Td> V </Td> <Td> Dark or "brown" type </Td> <Td> No </Td> <Td> Sometimes darkens </Td> <Td> 22--28 </Td> </Tr> <Tr> <Td> VI </Td> <Td> Very dark or "black" type </Td> <Td> No </Td> <Td> Naturally black - brown skin </Td> <Td> 29--36 </Td> </Tr> </Table>

What uv rays do you need to tan