Skin condition  

"But an important caution must here be entered. Natives speak with such horror about the various forms of ugliness, and repulsion is so clearly discernible in their behaviour that there is no temptation to doubt their word. In fact, in games and amusements, an albino, an idiot, or a man afflicted with skin disease is so completely left out of the fun that his loneliness and isolation wake pity even in the frigid heart of an ethnographer. Thus observation fully confirmed the verbal proposition in which all the natives are agreed, that all such people are absolutely debarred from sexual intercourse and that they have to resort to solitary means of satisfaction." --The Sexual Life of Savages (1929) by Bronisław Malinowski