Chapter 32: Overview of the Pigmentation Process

INTRODUCTION

Skin color results from the incorporation of melanin-containing melanosomes, produced by the melanocytes, into the keratinocytes in the epidermis and their ensuing degradation. Although other factors contribute to skin color, such as carotenoids or hemoglobin,¹ the amount, quality, and distribution of melanin present in the epidermis represent the primary sources of human skin color. The number of melanocytes in human skin is equal across humanity, thus, their activity and interaction with the keratinocytes emerge as the accountable factors for skin color.²

Melanin pigment is produced in the melanosome, an organelle located in the cytoplasm of melanocytes. When excess melanin is produced, disorders of pigmentation or dyschromia can result. Melanin production is stimulated by several factors including ultraviolet light, estrogen, melanocyte-stimulating hormones (MSH), stress, inflammation, injury, infrared light, and heat. The most common forms of dyschromia are melasma, solar lentigos, postinflammatory hyperpigmentation, and dark circles under the eyes.

Melasma, also known as chloasma or “mask of pregnancy,” refers to a very common condition that is usually seen in women of childbearing age. It is a chronic disorder that can be frustrating to patients and physicians because it often recurs, especially due to exposure to the sun or estrogen. Melasma presents as irregularly shaped, but often distinctly defined, blotches of light- to dark-brown pigmentation. These patches are usually seen on the upper lip, nose, cheeks, chin, arms, forehead, and neck.

Solar lentigos are caused by both acute and chronic exposure and manifest as macular brown lesions usually 1 cm in diameter. The face, shoulders, chest, back, and hands are the areas typically affected because they receive the most sun exposure.

Postinflammatory hyperpigmentation, also known as postinflammatory pigment alteration (PIPA), can present as a result of various skin disorders. Occasionally, therapies for skin disease can cause or exacerbate dyschromia, such as resurfacing lasers or chemical peels. This occurs more commonly in people with darker skin types.

The cause of dark circles under the eyes is poorly understood. Many believe that the thin skin in this area allows the blood vessels to become more visible. Any inflammation or vasodilation in this region may manifest as darkening.³ However, there also seems to be a pigmentary component that may be caused by excessive melanin production or deposition of the iron-storage complex hemosiderin from sluggish blood flow in the area. Unfortunately, there is no consensus about the best treatment of dark under-eye circles.

Disorders of pigmentation are best treated using a combination of ingredients including tyrosinase inhibitors, PAR-2 blockers, and exfoliating agents. These should be combined with ingredients such as lignin peroxidase and laser or light devices, which attack or target melanin. Antioxidants can also be used to prevent hyperpigmentation by hindering inflammation. Polyphenol antioxidants have been found to be strong chelators of metal ions, such as Fe²⁺, Fe³⁺, Cu²⁺, Zn^...