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Skin color is genetically determined and is caused by the total amount of melanin pigment in the skin. Normal constitutive melanin pigmentation determines skin type, which is currently classified by the Fitzpatrick phototypes as follows:

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Skin PhototypesAbility to TanSusceptibility to Burns
SPT INever tans, white skinSunburns easily
SPT IITans with difficultySunburns easily
SPT IIICan tan with timeOccasionally burns
SPT IVTans easilyRarely burns
SPT VTans easily, brown skinRarely burns
SPT VITans easily, black skinRarely burns
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Disorders of hypopigmentation are caused by decreased melanin content in the skin owing to decreased or absent melanin production or melanocytes. Disorders of hyperpigmentation are caused by increased melanin content in the skin owing to an increase in melanin production or melanocytes.

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Decreased or absent melanin in the skin can lead to hypomelanosis and can occur by two main mechanisms.

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1. Melanocytopenic hypomelanosis: absent or decreased number of melanocytes (e.g., vitiligo).

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2. Melanopenic hypomelanosis: absent or decreased melanin production, but normal number of melanocytes (e.g., oculocutaneous albinism).

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Pityriasis Alba

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Pityriasis alba is a common asymptomatic, sometimes scaly, hypopigmentation of the face, neck, and body.

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Insight

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Pityriasis alba entails both mild dermatitis and pigment alteration; generally, the former responds quickly while the latter continues to be an issue for many months or years.

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Epidemiology

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Age Young children, often between the ages of 3 and 16 years.

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Gender M = F.

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Race All races, more noticeable in darker skin types.

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Prevalence Common.

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Etiology Likely a form of atopic dermatitis.

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Pathophysiology

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Thought to be an eczematous dermatosis, with hypomelanosis resulting from postinflammatory changes and ultraviolet screening effects of the hyperkeratotic and parakeratotic epidermis.

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History

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Hypopigmented areas are usually stable then gradually disappear with age. Some lesions may persist into adulthood. The areas are typically asymptomatic, but can sometimes burn or itch.

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Physical Examination

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Skin Findings
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Type Macules, may have slight scale.

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Number One to twenty lesions may be present.

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Color Pink, then off-white to tan-white.

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Size and Shape 5 to 30 mm or larger.

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Distribution Face (malar region), neck, trunk, extremities.

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Sites of Predilection Face, especially the cheeks (Fig. 12-1), midforehead, and around the eyes and mouth.

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FIGURE 12-1
Graphic Jump Location

Pityriasis alba Faint, hypopigmented slight scaly macules located on the cheeks of a child.

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General Findings
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May ...

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