Background
Pityriasis alba (PA) is a relatively common skin disorder in children and young adults. It is characterized by the presence of ill-defined, scaly, faintly erythematous patches that subside to leave areas of hypopigmentation. Lesions may progress through the following 3 clinical stages:
- Papular (scaling) erythematous
- Papular (scaling) hypochromic
- Smooth hypochromic
Lesions eventually subside, leaving areas of hypopigmentation that slowly repigment to normal. The duration of pityriasis alba varies from one month to 10 years, but most cases resolve over several months to one year. Diagnosis is made clinically, and treatment consists of skin care and education of the parents about the benign nature of the disorder. Hydrocortisone may decrease erythema, scale, and pruritus, if present. Pityriasis alba is a nonspecific finding that is commonly associated with atopic dermatitis. Xerosis that presents in individuals with atopic diathesis is an important element in the development of the disease. The etiology is unknown.
Note the characteristic, ill-defined, hypopigmented macules in this 6-year-old child with pityriasis alba. 
Lesions of pityriasis alba are usually bilateral and located on the face, arms, and neck. 
The hypopigmentation produced by pityriasis alba may take a year or longer to return to normal. 
This older patient with areas of hypopigmentation on the face has a common problem that would be included in the differential diagnosis of pityriasis alba. Several months earlier, he had areas of irritant contact dermatitis on his cheeks. When those resolved, he was left with areas of postinflammatory hypopigmentation. These should eventually repigment to an even skin tone. Pathophysiology
In a study of 9 patients with extensive pityriasis alba, the density of functional melanocytes was reduced in the affected areas without any change in cytoplasmic activity.[1] The melanosomes tended to be fewer and smaller, but their distribution pattern in the keratinocytes was normal. Melanosomal transfer to keratinocytes was generally not disturbed. Histology was nonspecific. Hyperkeratosis and parakeratosis were not consistently present, and they are seemingly unlikely to play a significant role in the pathogenesis of the hypomelanosis. A variable degree of intercellular edema and intracytoplasmic lipid droplets were present. Hypopigmentation may be primarily due to the reduced numbers of active melanocytes and a decrease in number and size of melanosomes in the affected skin.
Epidemiology
Frequency
United States
Although the exact incidence has not been described, up to one third of school-aged children may have this disorder. Pityriasis alba is not seasonal, but the dry, slightly scaling appearance tends to worsen during cold months, when the air is relatively dry inside the home. In addition, sun exposure may make the lesions more obvious during spring and summer. The condition is more common in patients with a history of atopy.
International
In a large study of 9955 schoolchildren aged 6-16 years who lived in a tropical region, the prevalence of pityriasis alba was 9.9%.[2]
Mortality/Morbidity
Pityriasis alba is generally self-limited and asymptomatic. Cosmetic appearance may be an issue in some patients. Daycare facilities and schools may voice concern about the disorder and request the child be evaluated to rule out an infectious disease.
Race
Pityriasis alba occurs in people of all races. One study found the incidence to be slightly higher in light-skinned people. The condition is frequently more apparent and cosmetically bothersome in patients with darker complexions.
Sex
Pityriasis alba is more prevalent in males than in females.
Age
Pityriasis alba is most common in children aged 3-16 years. Ninety percent of cases occur in children younger than 12 years. Pityriasis alba occasionally occurs in adults.
Zaynoun ST, Aftimos BG, Tenekjian KK, et al. Extensive pityriasis alba: a histological histochemical and ultrastructural study. Br J Dermatol. Jan 1983;108(1):83-90. [Medline].
Bechelli LM, Haddad N, Pimenta WP, et al. Epidemiological survey of skin diseases in schoolchildren living in the Purus Valley (Acre State, Amazonia, Brazil). Dermatologica. 1981;163(1):78-93. [Medline].
In SI, Yi SW, Kang HY, Lee ES, Sohn S, Kim YC. Clinical and histopathological characteristics of pityriasis alba. Clin Exp Dermatol. Jul 2009;34(5):591-7. [Medline].
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Jorizzo J, Levy M, Lucky A, et al. Multicenter trial for long-term safety and efficacy comparison of 0.05% desonide and 1% hydrocortisone ointments in the treatment of atopic dermatitis in pediatric patients. J Am Acad Dermatol. Jul 1995;33(1):74-7. [Medline].
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Rigopoulos D, Gregoriou S, Charissi C, Kontochristopoulos G, Kalogeromitros D, Georgala S. Tacrolimus ointment 0.1% in pityriasis alba: an open-label, randomized, placebo-controlled study. Br J Dermatol. Jul 2006;155(1):152-5. [Medline].
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