or if not genetic it can be due to a lot of things like stress, malnutrition or lack of certain vitamins like A, E , zinc copper,Iron, selenium. But these usually can be found
in a multivitamin because you only need the zinc etc.
in trace amounts. If you are not absorbing nutrients right through the intestines that also possible. But, usually you see floating , fatty or glossy stools.
Another cause can be anemia. Have you had a complete blood count done?