This infant has multiple lesions of urticaria pigmentosa (UP), which is also called maculopapular cutaneous mastocytosis (MPCM). Lesions of UP are characterized by small, yellow-tan to reddish-brown macules or slightly raised papules. This child has the polymorphic type of UP, in which individual lesions vary in size and shape. Pruritus associated with UP may be exacerbated by changes in temperature, exertion, local friction, or certain medications. UP lesions, as well as other lesions rich in mast cells, may demonstrate Darier's sign, which is the development of a localized whealing and erythema within about five minutes following rubbing, scratching, or stroking of the lesion.