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Variations in Pigmentation and Ultrastructural Skin Differences Among Ethnic Groups
By: Rupa Pugashetti, MD, Santa Clara Valley Medical Center, and Howard I. Maibach, MD, University of California School of Medicine
Posted: September 1, 2010, from the September 2010 issue of Cosmetics & Toiletries.
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Erythemal response also was examined in patients of different complexions by Olson.18 The minimal erythema dose (MED) was determined in Caucasian and in different complexions of African-American skin. Among light, medium, and dark complected African-American skin, no minimal erythema response typically was found. Instead, a spectrum of responses was found that was directly proportional to the degree of pigmentation. Additionally, the average MED of darker-complected African-American skin was 33 times greater than that of Caucasian skin. Caucasian skin had the smallest amount of pigment and smallest melanosomes, which were mostly contained within melanosome complexes.
Further findings included the observation that melanosome size is directly proportional to the intensity of skin pigmentation, and darkly pigmented subjects have larger, wider and denser melanosomes. Generally, with increasing pigmentation, the size of melanosomes, the proportion of singly dispersed melanosomes, and the MED were all shown to increase. Authors suggested that the increased resistance of darker skin to the damaging effects of UV radiation may therefore be due to larger, more light-absorbing, individually dispersed melanosomes. Furthermore, melanosomes in darkly pigmented skin are degraded less by lysosomes, resulting in more light-absorbing bodies in the stratum corneum.19
Measuring Skin Color
The assessment of skin color or the effects of treatments on skin color has advanced with improvements in measurement devices, as are described here. Most of these devices are based on the L*, a*, b* system to determine skin color. As is generally known, L* represents skin reflectance or lightness, a* measures color saturation from red to green, and b* measures color saturation from yellow to blue.
Chromameter: Lee et al. evaluated a chromametera for the objective measurement of periocular and facial pigmentation in African-American, Caucasian and Hispanic subjects.20 Using the L*, a*, b* system, significant differences in L* were observed among all ethnic groups, while a* and b* were less sensitive to pigmentation differences. Additionally, the L* value demonstrated significant differences between Fitzpatrick skin types III–VI, the more heavily pigmented groups. The chromameter was found to reliably measure facial pigmentation; in addition, it showed good inter- and intra-instrument reliability.
Tristimulus colorimeter vs. narrow-band reflectometer: Shriver and Parra compared two methods to measure pigmentation in both the skin and hair of European-Americans, African-Americans, South Asians and East Asians.21 A tristimulus colorimeterb, again based on the L*, a*, b* color system, was compared to a narrow-band reflectometerc, which measures pigment in terms of erythema and melanin indices. Both instruments provided accurate estimates of pigment level in the skin. However, measurements performed by the narrow-band reflectometer were less affected by the greater redness of specific body sites due to increased vascularization. Thus, while both approaches were found to be accurate, pigmentation measurements using the narrow-band reflectometer may be more useful.