Lots of gentlemen still prefer blondes — and scientists with too much time on their hands have discovered why: They’re in relatively short supply.

Natural blondes, as opposed to the legions of “bottle blondes’’ who use dye, need 200 genes to create the color, the Sunday Times of London reports. That compares to 60 genes for brown tresses and only a handful for most redheads.

Naturally blond hair is rare. Only 12.7 percent of women are born with it. For men, the figure is 9.9 percent.

Britain’s Medical Research Council conducted the study, looking only at white people of European descent.