Melasma is a common acquired and chronic disorder of hyperpigmentation affecting up to 5 million Americans. It most often involves the face and women are more frequently affected than men. Those of African, Asian, or Hispanic descent with Fitzpatrick skin type III or greater are at higher risk for this condition. Melasma can negatively affect quality of life, especially in patients with lesser amounts of education and underlying psychological disease.

The pathogenesis of melasma is poorly understood but it is likely multifactorial and due to a combination of environmental exposures, hormones, and cellular factors such as cytokines. Ultraviolet (UV) light is an important inducer of melasma, evident by the fact that this condition occurs in sun-exposed sites and worsens with further exposure. Histopathologic evaluation shows larger and more prominently dendritic melanocytes rather than an increased density of these cells. Historically, this condition has also been strongly associated with increased levels of estrogen and progesterone and its onset is often reported during pregnancy and while taking oral contraceptives. Unfortunately, this relationship remains unclear and circulating levels of hormones do not correlate with the presence and severity of melasma.

Melasma most often occurs in young to middle-aged women with a prevalence that increases with age. It is characterized by symmetric, light to dark, or gray-brown patches with well-defined borders. Lesions may range from 0.5 cm to greater than 10 cm in diameter. The three categories of melasma localization include centrofacial, malar, and mandibular. The centrofacial type is most common with patches located at the forehead, cheeks, nose, upper lip, and chin (Figs. 28-1 and 28-2). The malar type is more limited with disease at the nose and cheeks, and, in mandibular disease, involvement is usually at bilateral rami. The condition has also been reported at the forearms and chest but this is less well described (Fig. 28-3).

When the disease first appears during pregnancy, it often resolves after childbirth, though this may be less frequent in women of darker skin types. When occurring in the context of an oral contraceptive, melasma often becomes more chronic in nature and can persist for years.

Most often, melasma can be diagnosed by history and physical examination alone. However, examination by Wood lamp may better characterize the condition, which has classically been described based on whether pigment appears to be epidermal, dermal, mixed, or indeterminate. Epidermal patches should be accentuated and dermal patches should become less obvious when exposed to the lamp. Traditionally, dermal disease has been considered
more difficult to treat. However, recent studies suggest that even in melasma that seems epidermal by Wood lamp examination, dermal melanin deposition is common. This may explain why the condition is oftentimes challenging to treat regardless of Wood lamp results.

At times the differential diagnosis may include postinflammatory hyperpigmentation, solar lentigines, ephelides, drug-induced pigmentation,
actinic lichen planus, lichen planus pigmentosus, facial acanthosis nigricans, frictional melanoses, exogenous ochronosis, erythema dyschromicum perstans, poikiloderma of Civatte, and bilateral acquired nevus of Ota-like macules (Hori nevus) (Table 28-1). When the diagnosis is unclear, biopsy may prove enlightening or rule out other disorders.