Why is hand washing so important? A new study may suggest a possible answer, as researchers have found thousands of species of bacteria live on our hands, with the typical hand having roughly 150 different species of bacteria living on it.

The Proceedings of the National Academy of Sciences study found women had a greater variety of bacteria on their hands than men. Overall, both men and women had more types of bacteria on their hands that it was previously thought.

The researchers, from the University of Colorado at Boulder, took samples from the hands of 51 college students and identified 4,742 different species of bacteria. Only five species were common among all 102 human hands in the study. Another interesting finding was that even the right and left palms of the same person shared an average of only 17 percent of the same bacteria species.

“The sheer number of bacteria species detected on the hands of the study participants was a big surprise, and so was the greater diversity of bacteria we found on the hands of women,” Dr. Noah Fierer, who led the research, was quoted as saying.

One possible explanation to the fact that women’s hands harbour more bacteria species that men’s is that men generally have more acidic skin than women, which provides a more harsh living environment for the microscopic bacteria. Other explanations are differences in sweat and oil gland production between men and women, the frequency of moisturizer or cosmetics applications, skin thickness or hormone production, the researchers said.

However, it is important to note that “the vast majority of the bacteria we have on our body are either harmless or beneficial… the pathogens are a small minority.”

So, ladies, don’t forget to wash your hands!