ABSTRACT
Introduction 604
UV-Induced Chemical and Biochemical Changes:
Causes and Consequences 605
Photosensitizer and Reactive Oxygen Species 605
Iron and Copper 605
Matrix-Degrading Metalloprotease 607
Antioxidant Defenses of the Skin 609
Antioxidant Defense Enzymes 609
Low Molecular Weight Antioxidants 610
Photoprotection of Human Skin Using Antioxidants and Other
Photoprotectants 611
Vitamin E and Its Derivatives 612
Vitamin C and Its Derivatives 614
Carotenoids 615
Plant Polyphenolics 617
Tea Polyphenols 618
Silymarin 618
Emblica Antioxidant 619
Combination of Antioxidants 620
Unconventional Photoprotectants 621
Selenium 622
Zinc 622
Chelating Agents 622
Compatible Solutes 623
Retinoids 623
Dihydroxyacetone 624
Commercial Products 624
Conclusions 624
References 629
INTRODUCTION
Sun is the great initiator of photochemical reactions, which provides energy
that sustains plant life and maintains human health. It warms the earth and
furnishes solar energy, and in humans, activates synthesis of vitamin D for
utilization by the body to help it absorb calcium and other minerals. As the
outermost barrier of the body, the skin is directly exposed to a pro-oxidative
environment. The effects of ultraviolet (UV) radiation from sun exposure can
induce or exacerbate oxidative attack leading to the generation of reactive
oxygen species (ROS) and other free radicals. The most severe consequence
of photodamage is skin cancer. Less severe photoaging changes result in
wrinkling, scaling, dryness, and uneven pigmentation consisting of hyper-
and hypopigmentation (1-3).
