Blond or fair hair is a hair color characterized by low levels of the dark pigment eumelanin. The resultant visible hue depends on various factors, but always has some yellowish color. The color can be from the very pale blond caused by a patchy, scarce distribution of pigment to reddish "strawberry" blond or golden-brownish "sandy" blond colors the latter with more eumelanin. Occasionally, the state of being blond, and specifically the occurrence of blond traits in a predominantly dark or colored population are referred to as blondism. Because hair color tends to darken with age, natural blond hair is significantly less common in adulthood. Naturally-occurring blond hair is primarily found in people living in or descended from people who lived in the northern half of Europe and may have evolved to enable more efficient synthesis of vitamin D , due to northern Europe's lower levels of sunlight.