Total tan 'impossible to perfect'
Sun-worshippers seeking an even all-over tan may be aiming for the impossible, a medical study has concluded.
Scientists at the University of Edinburgh found that some areas of the body are much more resistant to tanning than others.
They said their findings could explain why some holidaymakers find it so hard to achieve a consistent tan all over their body.
The research team carried out the study to find out why different types of skin cancer tend to be found in different parts of the body, even though they are all caused by exposure to harmful ultraviolet (UVB) rays from the sun.
They analysed the skin of 100 volunteers who were exposed to six doses of UVB on two areas of their body - their back and their buttocks.
After seven days, the volunteers' skin was analysed to find what colour remained after any redness had died down.
The colour, which we know as a suntan, comes from the skin's production of melanin, a defence which blocks the skin from absorbing too much harmful UVB radiation.
The scientists found that the buttocks were much more resistant to tanning, staying whiter than backs despite the same level of exposure.
The university said the study represents the first time that the depth of a person's tan, and not just skin redness, has been quantified.
Jonathan Rees, Professor of Dermatology at the University of Edinburgh, said he hoped the findings would help further understanding about skin cancer.