The researchers aren't sure why women harbored a greater variety of bacteria than men, but Fierer suggested it may have to so with the acidity of the skin. Knight said men generally have more acidic skin than women.
Other possibilities are differences in sweat and oil gland production between men and women, the frequency of moisturizer or cosmetics applications, skin thickness or hormone production, he said.
Women also may have more bacteria living under the surface of the skin where they are not accessible to washing, Knight added.
Asked if guys should worry about holding hands with girls, Knight said: "I guess it depends on which girl."
