The main color of normal skin is determined by three factors: 1. The content and distribution of various pigments in the skin; 2. The contents of oxygenated hemoglobin and reduced hemoglobin in skin blood; 3. The thickness of skin and the scattering phenomenon of light on the skin surface.
Pigments in the skin mainly include melanin and carotene. Skin contains melanocytes, which can produce melanin, which is the main factor to determine skin color. People of different races have different degrees of pigmentation, and the difference is mainly the amount of melanin produced, not the number of melanocytes. The color of human skin and hair depends not on the number of melanocytes, but on the number, size, distribution and melanogenesis of melanosome.
Asians belong to the yellow race, and their skin color is related to the carotene contained in their skin. Carotene is yellow and mostly exists in dermis and subcutaneous tissue. There are more hips in the chest and abdomen and fewer faces, so the skin color in the chest and abdomen is yellow. However, due to the influence of hemoglobin (hemoglobin) content in skin blood, facial skin color is pink. Oxyhemoglobin is bright red, and when it is hypoxic (reduced hemoglobin), it will turn dark red, and the skin color will change accordingly.
The color of skin is also influenced by the thickness of stratum corneum and the thickness of transparent layer and granular layer. If the stratum corneum is thick, the skin is yellowish; The granular layer and transparent layer are thick and the skin is white; In thin skin, due to the high light transmittance, the color of the underlying tissue can be displayed, and the red color of hemoglobin can be clearly seen on some people's cheeks. In the thicker part of the skin, the light transmittance is poor, and only carotene in the stratum corneum can be seen, so the skin is yellow. The yellowing of the skin of the elderly is due to the degeneration and fracture of elastic fibers in the dermis, the decrease of elasticity, and the poor blood supply to the skin.