Human skin aging is a natural phenomenon that results from continuous exposure to intrinsic (time, genetic factors, hormones) as well as extrinsic factors (UV exposure, pollution, tobacco). In areas that are frequently exposed to the sun, photoaging blends with the process of intrinsic aging, resulting in an increased senescent cells number and consequently accelerating the aging process. The severity of photodamage depends on constitutional factors, including skin phototype (skin color, tanning capacity), intensity, and duration of sunlight/UV exposure. Aging affects nearly every aspect of cutaneous biology, including pigmentation. Clinically, the phenotype of age pigmented skin has a mottled, uneven color, primarily due to age spots, with or without hypopigmentation. Uneven pigmentation might be attributed to the hyperactivation of melanocytes, altered distribution of pigment, and turnover. In addition to direct damage to pigment-producing cells, photodamage alters the physiological crosstalk between keratinocytes, fibroblasts, endothelial cells, and melanocytes responsible for natural pigmentation homeostasis. Interestingly, age-independent diffuse expression of senescence-associated markers in the dermal and epidermal compartment is also associated with vitiligo, suggesting that premature senescence plays an important role in the pathology.

中文翻译：

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老化过程中色素沉着系统的变化

人体皮肤老化是一种自然现象，是由于持续暴露于内在（时间、遗传因素、激素）和外在因素（紫外线照射、污染、烟草）而导致的。在经常暴露在阳光下的区域，光老化与内在老化过程相结合，导致衰老细胞数量增加，从而加速老化过程。光损伤的严重程度取决于体质因素，包括皮肤光型（肤色、晒黑能力）、强度和阳光/紫外线暴露的持续时间。衰老几乎影响皮肤生物学的方方面面，包括色素沉着。临床上，老年性色素沉着皮肤的表型具有斑驳、不均匀的颜色，主要是由于老年斑，有或没有色素减退。色素沉着不均匀可能是由于黑色素细胞的过度活化，改变了色素的分布和周转率。除了对色素生成细胞的直接损伤外，光损伤还改变了角质形成细胞、成纤维细胞、内皮细胞和负责自然色素沉着稳态的黑素细胞之间的生理串扰。有趣的是，真皮和表皮室中衰老相关标志物的与年龄无关的弥漫性表达也与白癜风有关，这表明过早衰老在病理学中起重要作用。