All-over body tan physically impossible
4 August 2010
MRC-funded researchers at the University of Edinburgh have found that an even tan may be impossible to achieve as some areas of the body are much more resistant to tanning than others.
The team carried out the study, published in the journal Experimental Dermatology, to assess why different kinds of skin cancer tend to be found in different parts of the body. The results showed that the human body is made up of different units of skin that respond differently to sunshine and which offer different degrees of protection against the harmful effects of sunshine.
Patches of skin of 100 volunteers were exposed to six doses of UVB on two areas of their body; their back and their buttock. The team found that the buttock is much more resistant to sunshine than the back, but when this skin does go red, it tans less well than other areas of the body. Having freckles also made it harder for a volunteer to achieve a suntan.
Within 24 hours of exposure to sunlight, skin normally has a rush of blood to the surface, causing redness. Researchers say this redness is often confused with the start of tanning, but in fact is the skin’s signal that it has been damaged.
After seven days, the volunteers’ skin was analysed to find what colour remained after the redness had died down. This colour, which we would recognise as a suntan, comes from the skin’s production of melanin, a defence that blocks the skin absorbing too much harmful UVB radiation.
Professor Jonathan Rees of the University of Edinburgh said:
“One of the real puzzles about melanoma is why the numbers of tumours differ so much depending on body site. Our work shows that in one sense we are all made up of different units of skin, which respond differently to sunshine, and which all may afford different degrees of protection against the harmful effects of sunshine.”
The research forms part of the MRC’s ongoing work to explore the body’s resilience to disease and degeneration, and to help researchers understand how this may be exploited to find new treatments for diseases such as cancer.