What is pityriasis alba?

What is Pityriasis Alba?

Pityriasis alba is a common, benign hypopigmentation disorder primarily affecting children and adolescents, characterized by superficial, hypopigmented macules or patches with fine scale, most commonly appearing on the face and upper extremities. 1

Clinical Characteristics

• Typical presentation: Round to oval hypopigmented patches, usually a few centimeters in diameter, with fine scale and ill-defined borders 1, 2
• Distribution: Most frequently affects the face, upper arms, neck, and trunk 1, 3
• Age group: Predominantly occurs in children and preadolescents, with equal incidence in boys and girls 3
• Skin type predilection: While it occurs in all skin phototypes, it is markedly more visible and commonly diagnosed in individuals with darker skin (phototypes III-VI) due to greater contrast with surrounding normal skin 1, 2
• Associated symptoms: Mild pruritus may be present, though many cases are asymptomatic 1, 2

Pathophysiology and Associated Conditions

• Strong association with atopic dermatitis: Pityriasis alba is considered by many experts to be a minor manifestation or milder form of atopic dermatitis 4, 1, 2
• Recognized as an associated feature: The American Academy of Dermatology lists pityriasis alba among the clinical associations that help suggest the diagnosis of atopic dermatitis, though it is too non-specific to be used as a defining criterion 4
• Histologic findings: Biopsy specimens consistently show spongiosis, follicular spongiosis, focal parakeratosis, acanthosis in the epidermis, and superficial perivascular lymphocytic infiltrate 3
• Mechanism: Poor cutaneous hydration and inappropriate melanin transfer appear central to pathogenesis, resulting in the characteristic hypopigmentation 2

Clinical Course and Triggers

• Natural history: Extended, multistage course with spontaneous remissions and recurrences over months to years 1
• Initial phase: Lesions may be preceded by subtle erythematous changes before hypopigmentation develops 1
• Exacerbating factors: Sun exposure increases the contrast between normal and affected skin, making lesions more cosmetically apparent and prompting patients to seek care 2
• Other potential triggers: Beauty treatments, xerosis, and possibly microorganisms have been reported, though etiology remains incompletely understood 1, 2

Differential Diagnosis

Critical distinctions to make:

• Pityriasis versicolor alba: Distinguished by positive KOH preparation showing hyphae and spores; Wood's lamp examination shows yellow-green fluorescence 5, 2
• Vitiligo: Shows complete depigmentation (chalk-white) rather than hypopigmentation, with sharply demarcated borders and no scale 2
• Nevus depigmentosus: Present from birth or early infancy, remains stable in size and distribution 2
• Nevus anemicus: Blanches with diascopy due to vascular abnormality rather than pigmentary change 2

Management Approach

First-line conservative management:

• Patient education: Counsel on proper skin care, adequate hydration, and use of emollients to address xerosis 2
• Photoprotection: Recommend broad-spectrum sunscreen (SPF 20 or higher) to minimize contrast between affected and normal skin 6
• Moisturizers: Regular application of emollients addresses the underlying poor cutaneous hydration 2, 6

Pharmacologic treatment when intervention is desired:

• Topical calcineurin inhibitors: Tacrolimus ointment 0.1% applied twice daily demonstrates statistically significant improvement in hypopigmentation, with complete resolution by 9 weeks in clinical trials 6
• Efficacy data: Tacrolimus reduced hypopigmentation scores from baseline 2.38 to 0.00 at week 9, significantly superior to moisturizers alone (P<0.001) 6
• Safety profile: Mild transient burning reported in 11.5% of patients; otherwise well-tolerated 6
• Topical corticosteroids: Low-potency corticosteroids may be used when inflammation is present, though evidence is limited 2

Important clinical caveats:

• The disorder is primarily of cosmetic significance with no systemic implications 7
• Many patients do not seek treatment due to the benign nature of the condition 7
• Spontaneous resolution typically occurs over time without intervention 1, 7
• Screen for and address underlying atopic dermatitis when present, as this may improve pityriasis alba 4, 1