Chapter 4 - The effects of sunlight on the skin of Asians

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Abstract

The Asian population consists primarily of mongoloids in East and South Asia and some Caucasians in East Central Asia. Although the population of Asia is more than half of the population of Earth, the inherent characteristics of Asian skin has not been investigated well as compared with those of Caucasian white skin. The skin color of Asians ranges from light brown to dark brown. We will discuss the functional characteristics of the melanin pigmentary system of Asian skin, and the differences from those of Caucasian skin. As Asian skin is more pigmented, the acute and chronic cutaneous responses to UV irradiation seen in brown skin differ from those in white skin. This chapter also provides an outline of the characteristic features of the acute and chronic effects of sunlight on the brown skin of Asians with respect to erythema, pigmentation, photoaging and skin cancer.

Introduction

There are three main races on earth, namely Mongolian, black African and Caucasians, which account for over 90% of the world's population [1]. Mongoloids include the peoples of East Asia, Indonesia, Polynesia, native Americans and Eskimos. The skin color of mongoloids is brown. Their body hair is scant and scalp hair is straight and black [2., 3.]. Caucasians include North Americans, Europeans, peoples of the Mediterranean region, the Middle East and most of the Indian subcontinent. Caucasians show wavy hair, abundant facial and body hair and a narrow nose. Their skin color is usually white, whereas peoples of the Middle East and Indians have brown skin color [4, 5]. Negroid peoples include the black people of Africa, who usually show dark pigmentation, tightly curled hair and a broad nose.

The population of Asians consists mostly of mongoloids in East and South Asia and some Caucasian in Middle East Asia. Their skin color ranges from light to dark brown. The people of the Far East and South Asian countries such as Korea, Japan, China, Singapore etc., look very similar and it is hard to differentiate them from each other.

At the beginning of this new millennium, the entire population of Earth is just slightly more than 6 billion. The population of Asia is around 3.7 billion, some 60% of total population (China has 1.2 billion, India 1.0 billion, Indonesia 200 million, Pakistan 156 million, Bangladesh 129 million, Japan 126 million, Vietnam 79 million, Philippines 76 million, South and North Korea 71 million, etc.). Although the population of Asia is more than half of the total population of Earth, the inherent characteristics of Asian skin have not been well investigated as compared with Caucasian white skin.

There are racial/ethnic differences in the genetic characteristics, as well as structure and function, between the brown skin of Asians and the white skin of Caucasians [6]. As Asian skin is more pigmented, the acute and chronic cutaneous responses to UV irradiation in brown skin differ from those seen in white skin. Recently, Asian countries have developed economically and their people have begun to pay more attention to the cosmetic problems of their skin. The commercial markets for cosmetics and drugs for the prevention and treatment of photodamaged and aged skin are increasing very rapidly in many Asian countries. Many investigators in the field of dermatology and cosmetology have become interested in the brown skin of Asians. So far, however, there have been few studies concerning the physiological and histological characteristics of Asian skin, the processes of aging and photoaging in brown skin, and the differences from those of Caucasian skin. Because the populations of Asia consist of various races, live in various regions with differing environments, and have a wide range of skin color from light brown to dark brown, it seems to be difficult or impossible to draw conclusions that can be applied to all Asians. The author is familiar with the brown skin of the people of East Asia, such as Korea, Japan, and China. So far, there have been many studies concerning UV response in human skin, particularly the white skin of Caucasians, while there have been few studies done on the brown skin of Asians and Hispanics, and on the black skin in African Americans. In this chapter, the acute and chronic effects of sunlight on the brown skin of Asians with respect to erythema, pigmentation, photoaging and skin cancer will be discussed.

Section snippets

Constitutive and facultative skin color in Asians

The melanin pigmentation of human skin is divided into two components: constitutive and facultative pigmentation. Constitutive skin color is the amount of cutaneous melanin pigmentation generated according to cellular genetic programs, without any direct effect from radiation of solar origin. Facultative skin color includes the short-lived immediate tanning and delayed tanning reactions, both of which are generally elicited by direct exposure of the skin to UVR [7].

Acute UV responses in Asians

The major acute clinical effects of UVR on human skin are well established in the white skin of Caucasians, and comprise sunburn inflammation (erythema) and tanning (pigmentation).

Chronic UV responses in Asians

Chronic exposure to UVR causes photoaging and skin cancer. In both developed and developing countries, the number and proportion of older people is increasing [32]. Most of the cutaneous changes attributed to aging in sun-exposed skin are, in fact, due directly to chronic UV effects on the skin. It has been estimated that 80% of the cutaneous changes observed in photodamaged skin could be prevented by protection against UV during life [33, 34, 35]. The incidence and mortality of skin cancers

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