Pityriasis alba is a common mild dermatitis/eczema of round or oval slightly scaly pink patches which leave pale ("hypopigmented") marks after the pinkness/redness has faded.
Pityriasis alba affects mainly children, and some young adults, especially on the cheeks and upper arms.
It becomes most apparent in summer, particularly in children with darker skin.
The areas of inflamed skin (typically eczema) don't develop a tan while the surrounding skin does, giving the appearance of a relative paleness to the skin.
Treating pityriasis alba involves using thicker moisturizers to the affected area, and often a mild steroid or topical calcineurin inhibitor such as tacrolimus or pimecrolimus for 1-2 weeks.
The colour eventually evens out over several months; it is rarely a permanent loss of colour.