CHAPTER 6: Pigmentation and Photoaging

Casual comparison of the appearance and texture of unprotected photoexposed hand and face skin versus the skin of the secluded upper inner arm quickly reveals the striking impact of accumulated solar radiation on skin aging, particularly after the third or fourth decade of life. The basis of this change in superficial appearance can be revealed in a host of anatomical, histological, and ultrastructural changes in the epidermis and dermis of the skin, which result from alterations at the cellular and molecular levels. There is increasing evidence that environmental pollution (including exposure to car fuel-derived particulates with/without light activation) and even certain wavelengths of visible light can also contribute to the global ‘photoaging’ response. Evolution has equipped human skin with at least partially effective protective devices against such environmental damage; principal among them includes the synthesis of copious amounts melanin that acts as a near-universal stress absorber. This still-enigmatic indole biopolymer acts as a ‘sink’ for toxins, pollutants, drugs, as well as a redox buffer against a host of reactive oxygen species. The latter are derived from a raft of chemical reactions at the skin. Brown/black (or wild-type) melanin far outperforms the photolabile red/yellow pheomelanin, which increases the vulnerability of the skin to photodamage and therefore photocarcinogenesis. Interventions that can boost eumelanin levels, in a solar radiation-independent manner, may enhance protection against skin photodamage.