Is Asian Skin Really Different from Black or Caucasian Skin?

Feb 1, 2010 | Contact Author | By: Johann W. Wiechers, PhD, JW Solutions
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Title: Is Asian Skin Really Different from Black or Caucasian Skin?
racex absorptionx barrier integrityx TEWLx sensitivityx pore sizex
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Keywords: race | absorption | barrier integrity | TEWL | sensitivity | pore size

Abstract: It often is claimed, particularly in East Asia, that Asian skin is more sensitive than Black or Caucasian. To explore this claim, the author investigates the current literature in this review and concludes there are two aspects being overlooked: the skin’s capability to cope with perturbations and the route of penetration.

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JW Wiechers, Is Asian skin really different from Black or Caucasian skin? Cosm & Toil 125(2) 66-73 (Feb 2010)

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It is often claimed that Asian skin is different from Black or Caucasian skin. This claim is so persistent throughout Asia, particularly East Asia, that it leads one to think there must be a physiological basis for it. Reviews such as the keynote presentation by Tony Rawlings at the 2005 IFSCC Conference provide a good overview of potential differences, but before discussing these, it would be beneficial to compare human skin with animal skin first.

Pig (ear) skin is generally believed to be the best model for human skin since its skin penetration characteristics and many other physiological parameters are roughly the same, or at least not very different. Based on this work, the authors concluded that “the results obtained (on pig ear skin) are similar to those of human skin, indicating the suitability of this porcine tissue as a model for human skin.”

Of course, skin is more than a series of external observations. The skin lipid composition (qualitative and quantitative) and its packing are important for optimal barrier function. Early work by Bouwstra et al. has indicated that pig skin exhibits liquid and hexagonal packing, yet the orthorhombic stratum corneum (SC) lipid packing phase has been identified as being critical to human skin barrier function. Nevertheless the barrier function of the two has been described as quite similar. In a review, Barbero and Frasch found that when the in vitro permeability of pig and human skin were compared, the correlation coefficient r was 0.88 (p < 0.0001) for the 41 compounds studied. They also found that the coefficient of variation of skin permeability (i.e., standard deviation divided by the average) was 21% for pig and 35% for human skin.

Within human subjects, percutaneous absorption studies of different racial skin types have also been conducted. These studies require many subjects to be statistically significant due to the high coefficient of variation in the permeability of human skin. In addition, different chemicals penetrate skin via different routes. Therefore, another way to characterize skin barrier function is to measure transepidermal water loss (TEWL) but this is not exactly the same. Percutaneous absorption relates to the outside-in barrier and applies to all chemicals, whereas the TEWL relates to the inside-out barrier and applies only to water. A third approach is to examine differences in clinical effects of the same application among different races; for instance, after applying an irritant. In the present paper, the author addresses these three possible methods to identify the existence of racial influences on human barrier function.

Race and Percutaneous Absorption

The subject of race and percutaneous absorption was popular in the 1980s but few papers have since emerged in the scientific literature. It is also highly unusual that most investigations of this aspect of skin penetration were performed in vivo. The oldest reference relating to this subject is from December 1978, when the percutaneous penetration of tritium-labeled diflorasone diacetate was examined in three Black and three Caucasian subjects. In the end, no marked differences were found.

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Table 1. Comparison of physiological characteristics between human skin and pig ear skin

Table 1. Comparison of physiological characteristics between human skin and pig ear skin

Pig (ear) skin is generally believed to be the best model for human skin since its skin penetration characteristics and many other physiological parameters are roughly the same, or at least not very different. Here are shown some of these physiological characteristics; data from Reference 2.

Table 2. Basal barrier function and stratum corneum integrity in different groups

Table 2. Basal barrier function and stratum corneum integrity in different groups

Basal barrier function and stratum corneum integrity in different groups; integrity is measured as the number of tape strippings required to disrupt the barrier; modified from Reference 21.

Table 3. Lag times after application of methyl nicotinate

Table 3. Lag times after application of methyl nicotinate

For untreated skin, the barrier function in Black skin > Caucasian skin (p < 0.05) > Asian skin (p < 0.01), where the number in parentheses is the level of significance relative to Black skin; reproduced from Reference 30.

Figure 1. The effectiveness of the human skin barrier depends on the composition of the stratum corneum lipids as well as their packing

Figure 1. The effectiveness of the human skin barrier depends on the composition of the stratum corneum lipids as well as their packing

The skin lipid composition (qualitative and quantitative) and its packing are important for optimal barrier function; reproduced from Reference 3.

Figure 2. Influence of race on the percutaneous absorption of benzoic acid, caffeine and acetyl salicylic acid

Figure 2. Influence of race on the percutaneous absorption of benzoic acid, caffeine and acetyl salicylic acid

Influence of race on the percutaneous absorption of benzoic acid, caffeine and acetyl salicylic acid in: Caucasian (C), Black (B) and Asian (A) subjects; reproduced from Reference 11.

Figure 3. Relationship between TEWL and skin temperature in samples of Caucasian and Black skin in vitro

Figure 3. Relationship between TEWL and skin temperature in samples of Caucasian and Black skin in vitro

TEWL, which is strongly influenced by environmental effects and eccrine gland activity, i.e., sweating, was measured as a function of skin temperature, and it was concluded that TEWL in Black skin was higher than in Caucasian skin; reproduced from Reference 17.

Figure 4. Skin type changes in basal barrier function and stratum corneum integrity

Figure 4. Skin type changes in basal barrier function and stratum corneum integrity

Figure 4. Skin type changes in basal barrier function and stratum corneum integrity; subjects with skin type V/VI displayed significantly greater stratum corneum integrity, as assessed by tape-stripping (p < 0.001); reproduced from Reference 2.

Figure 5. Degree of self-estimated stinging

Figure 5. Degree of self-estimated stinging

Degree of self-estimated stinging; mean value of difference between lactic acid and water, evaluated after 2, 4 and 5 min; reproduced from Reference 24

Figure 6. Stinging test

Figure 6. Stinging test

Stinging test: Chromameter Δa*-values of Japanese and German subjects for water and lactic acid (mean of all evaluation times); reproduced from Reference 24.

Biography: Johann W. Wiechers, PhD, JW Solutions

Johann W. Wiechers, PhD

A pharmacist by training, Johann W. Wiechers, PhD, earned his doctorate in 1989 in skin penetration enhancement at the University of Groningen, The Netherlands. Following six years at Unilever in the UK, he joined Uniqema in 1995 as skin R&D director. Wiechers founded JW Solutions, a consultancy focused on various aspects of cosmetic science, and released "Formulating for Efficacy, the Software", a computer program to help you deliver your active ingredients more effectively. Johann is no longer with us, but the work he started will continue just as he would have wished.

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