The color of human skin varies from the darkest brown to the lightest shades. Variation in pigmentation, which is a result of genetics (inherited from one’s biological parents), sun exposure, or both, causes differences in skin color across individuals. Because of variances in the environment, distinctions between groups emerged through natural selection and govern the biochemical consequences of UV light penetrating the skin.
Many components influence the actual skin color of various persons, but the pigment melanin is by far the most important. Melanin is produced by cells called melanocytes in the skin and is the primary determinant of skin color in people with darker skin. The bluish-white connective tissue underneath the dermis and the hemoglobin circulating in the dermal veins define the skin tone of those with light skin. When arterioles dilate as a result of physical exertion or sexual desire, or when the nervous system is stimulated (anger, embarrassment), the red hue beneath the skin becomes more noticeable, especially in the face.