ABSTRACT
Introduction 511
Skin-Whitening Ingredients 513
General Properties of EA 514
Existence 514
Physicochemical Properties 514
Biochemical Properties 514
Skin-Whitening Activity in Humans 515
Preventing Skin Pigmentation after Sunburn 515
Improving Effect on Skin-Pigmentation Conditions 515
Mode of EA Activity 516
In Vivo Experience 516
In Vitro Experience 517
Summary 520
References 520
INTRODUCTION
Spots and freckles represent general skin-pigmentation conditions that are caused
by enhancing and continuous melanogenesis (melanin synthesis). Melanin,
the root factor in such conditions, is synthesized from tyrosine in epidermal
melanocytes (pigment cells) via numerous enzymatic and nonenzymatic oxi-
dation and polymerization processes (Fig. 1). Melanin is incorporated into
vicinal keratinocytes and determines skin coloration. Keratinocytes containing
melanin are discarded through the process of keratinization (Fig. 2). Melano-
genesis is enhanced by stimuli such as sunburn [overexposure to ultraviolet
(UV) light]. [For the textbook about melanin and its related matters, see Refs.
(1) and (2).]
