WELL, DUH:

Women's bare flesh in winter is a bigger turn-on for men, says a new research.
 
To reach the conclusion, a group of male subjects were asked, at different times of the year, to rate photos of women. They gave their highest scores in the winter and autumn, and their lowest scores in the summer.
 
Researchers at University of Wroclaw in Poland who carried out the experiment believe the seasonal variation may have an impact on mate choice and on levels of adultery.
 
There is no clear explanation for the variation, but the researchers say one theory is that fewer female bodies are on display in the winter, so the rarity makes them more attractive.