Voegeli R, Rawlings A V, Summers B
DSM Nutritional Products Ltd., PO Box 2676, Bldg. 203.4/86, 4002, Basel, Switzerland.
Int J Cosmet Sci. 2015 Apr;37(2):241-52. doi: 10.1111/ics.12189. Epub 2015 Jan 21.
Hypotheses have been developed for the evolutionary selection of skin pigmentation one of which relates to improved skin barrier function. The aim of this study was to compare facial skin condition on photoexposed (cheek) and photoprotected (post-auricular) sites of naturally pigmented subjects of different ethnicities (Fitzpatrick skin phototypes II/III and V/VI) and Albino African subjects to understand better the relationship between facial stratum corneum (SC) barrier function, skin surface pH and skin pigmentation.
Expert grading of skin conditions, capacitance, skin surface pH and skin barrier function measurements were performed. For the latter, transepidermal water loss (TEWL) measurements before (basal TEWL), after 3, 6 and 9 consecutive tape strippings (SC integrity) and 3.5 and 24 h post tape stripping (barrier recovery) were taken. Amounts of SC protein removed during stripping were estimated using infrared densitometry (SC cohesion).
Firstly, correlation analysis of the biometric data of the Black African and Caucasian subjects showed there to be no relationship between skin surface pH and ITA° values nor pH and ITA° with basal TEWL. Neither skin surface pH nor ITA° correlated with SC integrity and barrier recovery measurements, but skin surface pH correlated with SC cohesion. ITA° values were correlated with skin hydration. Secondly, on comparing the three ethnic groups, severe skin photodamage was observed in the Albino African subjects and their SC was thicker. Whereas their basal TEWL was elevated, superior values for SC integrity and barrier recovery were measured. No differences in basal TEWL, SC integrity and barrier recovery were found between the other two subject groups. Equally, SC cohesion and skin surface pH values were similar among the three groups.
There was no relationship between ITA° values and basal TEWL, SC integrity, SC cohesion and barrier recovery, but ITA° was correlated with skin hydration. Skin surface pH, irrespective of ITA° values, correlated with SC cohesion, indicating a greater intracorneal cohesion at lower pH values. Thus, pigmentation has no effect on SC barrier properties but was related to skin hydration. On comparing the three ethnic groups, Albino African SC was found to be superior to the Caucasian and Black African subjects in terms of SC integrity and barrier recovery but not basal TEWL. The Albino African subjects also have a thicker SC which contributes to their better SC integrity. No differences in skin barrier functionality or skin surface pH were observed for the other two groups. Skin hydration was, however, greatest in the Black African subjects. Our data support the evolutionary hypothesis that pigmentation protects the skin from UV irradiation and thereby the skin barrier but not the skin pigmentation-/pH-driven adaptive skin barrier hypothesis.
关于皮肤色素沉着的进化选择已提出多种假说，其中之一与皮肤屏障功能的改善有关。本研究的目的是比较不同种族（Fitzpatrick皮肤光类型II/III和V/VI）的自然色素沉着受试者以及白化病非洲受试者面部暴露于光照部位（脸颊）和受光保护部位（耳后）的皮肤状况，以更好地了解面部角质层（SC）屏障功能、皮肤表面pH值与皮肤色素沉着之间的关系。
进行了皮肤状况的专家分级、电容测量、皮肤表面pH值测量以及皮肤屏障功能测量。对于皮肤屏障功能测量，在连续进行3次、6次和9次胶带剥离前（基础经表皮水分流失，TEWL）、之后以及胶带剥离后3.5小时和24小时（屏障恢复）测量经表皮水分流失。使用红外密度测定法估计剥离过程中去除的SC蛋白量（SC内聚力）。
首先，对非洲黑人和白人受试者的生物特征数据进行相关性分析表明，皮肤表面pH值与ITA°值之间以及pH值和ITA°值与基础TEWL之间均无关系。皮肤表面pH值和ITA°值均与SC完整性和屏障恢复测量值无关，但皮肤表面pH值与SC内聚力相关。ITA°值与皮肤水合作用相关。其次，比较这三个种族群体时，在白化病非洲受试者中观察到严重的皮肤光损伤，并且他们的SC更厚。虽然他们的基础TEWL升高，但测量到的SC完整性和屏障恢复值更高。在其他两个受试者组之间未发现基础TEWL、SC完整性和屏障恢复方面的差异。同样，三组之间的SC内聚力和皮肤表面pH值相似。
ITA°值与基础TEWL、SC完整性、SC内聚力和屏障恢复之间没有关系，但ITA°与皮肤水合作用相关。无论ITA°值如何，皮肤表面pH值与SC内聚力相关，表明在较低pH值下角膜内聚力更大。因此，色素沉着对SC屏障特性没有影响，但与皮肤水合作用有关。比较这三个种族群体时，发现白化病非洲受试者的SC在完整性和屏障恢复方面优于白种人和非洲黑人受试者，但基础TEWL方面并非如此。白化病非洲受试者的SC也更厚，这有助于其更好的SC完整性。在其他两组中未观察到皮肤屏障功能或皮肤表面pH值的差异。然而，非洲黑人受试者的皮肤水合作用最强。我们的数据支持色素沉着可保护皮肤免受紫外线辐射从而保护皮肤屏障的进化假说，而不支持皮肤色素沉着/ pH驱动的适应性皮肤屏障假说。
