The Skin Colour Continuum
There is extensive variation in pigmentation between different human populations; measurements of skin colour in subjects
throughout the world reveal a continuum of colour,
ranging from the very lightest to the very darkest.
1: Skin colour varies within the same ethnic group
Researchers established six skin colour categories [1]
by measuring the facial colour of 8,452 women living in different geographical regions. This study demonstrated the diversity of skin colour and the range of variations. This classification of the skin colour of women
living in different geographical regions provides an overview of the diversity of skin colour worldwide. It shows that a given ethnic group is not
characterised by one specific colour. For example, the different Caucasian skin types in France, the USA and Russia are fair, intermediate
and tan. Women of African origin in France and the USA have tan, brown or dark skin. Hispanic women have a wide range of skin colours, from
fair to brown. In Japan, Korea and China, skin is fair to intermediate, while in India, it ranges from fair to dark.
2: Skin colour is based on melanin quality and quantity
Pigments are produced by specialised cells known as melanocytes and stored invesicles known as melanosomes. Pigmentation is not related to the number of pigment-producing cells, which is relatively similar from one ethnicity to another. Variations are due primarily to the quantity and quality of melanin (phaeomelanin and/or eumelanin) produced, as well as the size, mode of transfer, degradation and distribution of melanosomes within the keratinocytes.
3: UV sensitivity correlates with skin colour type [2, 3]
When skin biopsies are exposed to increasingly high doses of ultraviolet (UV) radiation in order to study the damage to skin cells (keratinocytes and melanocytes), the results in fair, intermediate and tan skin show that DNA damage can affect all the cells in the epidermis, including those in the basal layer, as well as cells in the superficial dermis. The damage is limited to the superficial layers of the epidermis in brown and dark skin.
Melanin levels are inversely correlated with the risk of skin cancer, including melanoma: the darker the skin, the lower the risk of developing skin cancer. However, the mortality rates amongst those with darker complexions are higher than their Caucasian counterparts. The five-year survival rates for African-Americans is significantly lower thant that of Caucasians (78% vs 92%) [4]
[1] de Rigal J, et al. Development and
validation of a new Skin Color Chart.
Skin Res Technol. 2007; 13: 101–109
[2] Del Bino S, et al. Relationship
between skin response to ultraviolet
exposure and skin color type. Pigment
Cell Res. 2006; 19 (6): 606–614
[3] Del Bino S, et al. Assessment of
ultraviolet radiation-induced DNA
damage within melanocytes in skin of
different constitutive pigmentation.
Br J Dermatol. 2013; 168 (5): 1120-
1123
[4] Wu XC , et al. Racial and ethnic
variations in incidence and survival
of cutaneous melanoma in the
United States, 1999–2006. J Am Acad
Dermatol 2011; 65:S26–37.
