The skin is not only subject to chronological aging: in fact, unlike the other organs of the body, it is directly affected by environmental stressors (1) such as sun, long term exposure to UV radiation (photoaging), and high levels of pollution. These environmental damaging agents are not only among the major skin cancer-promoting factors (2), but they also cause a progressive degradation of the dermal layer (3) resulting in premature aging, wrinkles, altered pigmentation, and loss of skin firmness (4).
Hyperpigmented spots and heterogeneities in the skin pigmentation are one of the main signs of skin aging (3). As found by the results of a recent publication, pigmentation disorders and heterogeneity are purely linked to UV-exposure, independently to the age: sun-induced damages appear to be responsible for about 80% of the facial aging signs when it comes to the skin of Caucasian women (3).
Photoaging (sun-induced aging), therefore, is the primary factor in skin aging and it is a cumulative process whose impacts depend on the degree of exposure to UV-radiation from sunlight and on the skin pigmentation. Some people are at higher risk, experiencing stronger degrees of photoaging: those who live in geographically warmer climates, who have outdoor lifestyles, and individuals whose skin is lightly pigmented (1). Moreover, a study comparing Chinese and European populations´skin revealed how the intensity of hyperpigmented spots appears to be a more prominent sign of aging in Chinese women (severe for 30% of women over 40) compared to Caucasian (French) women (severe for less than 8% of them, irrespective of age). (5)
Several studies revealed that chronic sun exposure causes fundictional losses and reduces proliferative capacity at the cellular level between infancy and adulthood, as well as causing futher losses  between early and late adulthood (6). Photoaged skin also shows alterations and damages in the collagen levels of connective tissue: the degradation of type I Collagen was increased by 58% in UV-irradiated skin in comparison with non-irradiated skin (4) in a scientific study that analyzed the two situations. Collagen fibers, constituents of the dermis - the layer providing support to the outer layer of the skin, the epidermis (6) - give strenght and resiliency to the skin (7). Collagen in the dermis is degraded by an agent called metalloproteinases, whose levels are highly increased with multiple UV-radiation exposure (4).
The traditional depigmenting treatments for hyperpigmented skin spots include hydroquinone, corticosteroids, and kojic acid. These agents are highly effective but they raise several safety concerns with long-term usage (e.g. atrophy, carcinogenesis, and other side effects). (8) Retinol appears to provide benefits that contribute to achieving a more omogeneous pigmentation, although it does not have direct skin-lightening properties: it improves the skin cells regeneration and the proliferation of  keratinocytes. (9) Several natural active compounds derived from plants and botanical extracts were identified over the last decades as potential depigmenting ingredients for topical treatments: arbutin, aloesin, gentisic acid, flavonoids, hesperidin, licorice, niacinamide, yeast derivatives, and polyhenols (8) constitute some examples. Many studies and publications support the hypothesis that natural plant extracts constitute an effective and safer alternative to traditional skin-lightening treatments, and incorporating these natural ingredients in topicaly applied cosmetics or cosmeceuticals significally expands the offer, providing always better treatments for hyperpigmented spots and uneven skin pigmentation. (8)
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(1) Fisher GJ., Kang S., Varani J., et al. (2002) „Mechanisms of Photoaging and Chronological Skin Aging“, Arch Dermatol., vol.138, n.11, pp.1462–1470
(2) Balasubramanian S., Eckert R.L. (2007) „Keratinocyte proliferation, differentiation, and apoptosis – differential mechanisms of regulation by curcumin, EGCG and Apigenin“, Toxicology and Applied Pharmacology, vol.224, n.3, pp.214–219
(3) Flament F., Bazin R., Laquieze S., Rubert V., Simonpietri E., Piot B. (2013) „Effect of the sun on visible clinical signs of aging in Caucasian skin“, Clinical, Cosmetic and Investigational Dermatology, vol.6, pp.221–232
(4) Fisher G.J., Wang Z., Datta S.C., Varani J., Kang S., Voorhees J. J. (1997) „Pathophysiology of Premature Skin Aging Induced by Ultraviolet Light“, N Engl J Med, vol. 337, pp.1419-1429
(5) Nouveau-Richard S., Yang Z., Mac-Mary S., Li L, Bastien P., Tardy I., Bouillon C., Humbert P., de Lacharrière O., „Skin ageing: a comparison between Chinese and European populations: A pilot study“ (2005) Journal of Dermatological Science, vol.40, n.3, pp.187-193
(6) Gilchrest B. (1989) „Skin aging and photoaging: An overview“,Journal of the American Academy of Dermatology, vol. 21, n.3, part 2. pp.610-613
(7) Uitto J. Collagen. In: Fitzpatrick TB, Eisen AZ, Wolff K, Freedberg IM, Austen KF, eds. (1993) “Dermatology in general medicine”, 4th ed., vol. 1, New York: McGraw-Hill, pp.299-314
(8h) Zhu W., Gao J. (2008) „The Use of Botanical Extracts as Topical Skin-Lightening Agents for the Improvement of Skin Pigmentation Disorders“, Journal of Investigative Dermatology Symposium Proceedings, vol.13, n.1, pp.20-24
(9) Yoshimura K., Tsukamoto M., Okazaki M., Virador V.M., Lei T., Suzuki Y., Uchida G., Kitano Y., Harii K. (2001) „Effects of all-trans retinoic acid on melanogenesis in pigmented skin equivalents and monolayer culture of melanocytes“, Journal of Dermatological Science, vol.27, supplement 1, pp.68-75