The Harlequin phenomenon.

The Harlequin phenomenon (HF) is a rare event that consists of a sudden paroxystic change in skin colour, resulting in two different body colours. It is most common in the newborn and can be a generalized phenomenon or only involve a specific body area. The HF of the newborn is thought to be secondary to a relative hypothalamic control immaturity of the sympathetic peripheral vascular tonus, although it has also been described in other age groups, primarily located to the face and neck and mostly caused by a sympathetic disautonomy. While certainly peculiar, the HF is a benign event in the newborn. Beyond this age the search for an underlying cause should be vigorously pursued.