Pityriasis alba is chronic in nature and recurrences occur over months to years. Lesions are usually asymptomatic, but cosmetically noticeable. The lesions are generally multiple, but few in number, and ranging from 5 to 30 mm with indistinct borders. The lesions may be initially erythematous, but generally are flesh-coloured with mild hypopigmentation and fine overlying scale. Hypopigmentation is accentuated by tanning, because of differentially superior tanning of naturally pigmented skin. These hypochromic lesions demonstrate only partial loss of pigment with Woods’ lamp and are generally limited to the cheeks, peri-oral area, forehead, trunk and proximal arms, and far less frequently on the legs [9,10,19]. A more extensive and persistent form of pityriasis alba-like hypopigmentation has been described in older patients and termed extensive pityriasis alba; however, it is unclear as to whether this entity is a related illness or a form of progressive macular hypomelanosis .
The course of pityriasis alba is variable and recurrent lesions may develop. Individual lesions may last for years, but usually resolve spontaneously within a few months. Lesions generally resolve without sequelae, only to become clinically obvious again with seasonal tanning in sunny months. Most lesions will disappear before puberty. The condition is self-limited with excellent prognosis for repigmentation.
The differential diagnosis of pityriasis alba includes atopic dermatitis with postinflammatory pigmentary alteration, vitiligo vulgaris, postinflammatory pigmentary alteration, progressive macular hypomelanosis, tinea versicolor, discoid (nummular) eczema, tinea facei/tinea corporis, psoriasis, pityriasis rosea and pigmentary mosaicism. A rare diagnosis that is seen in developing nations in tropical and sub-tropical climates such as Africa, Asia and Latin America is leprosy. The indeterminate type can present with hypochromic and anaesthetic macules, alopecia of the eyebrows, thickening of the nerves, sensory disturbances, adduction of the little finger and facial paralysis . Aside from testing for sensory alterations, biopsy may be required to differentiate pityriasis alba from leprosy in selected settings.