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Blaschko's lines, also called the lines of Blaschko, are whorls, patches, streaks or lines in a linear or segmental distribution over the skin due to a mosaic skin condition. They can be observed in a variety of congenital and acquired skin disorders and follow embryonic cell migration pathways. Because they do not follow any vascular or neural elements of the skin, it has not been easy to define exactly what they are. It is characterized by a V-shape on the back, an S-shape on the front of the body and spirals on the back of the head.

Following Alfred Blaschko’s 1901 findings of lines and whorls in certain skin conditions, these Blaschko’s lines are now known to result from mosaicism. In 1961, Mary Lyon worked on striped patterns in female mice and postulated that all women were functional mosaics with regard to the X chromosome. By 1965, Lyon’s theories were used to explain patterns of skin lines in the Incontinentia pigmenti and ten years later used to explain why skin lesions follow lines of Blaschko in heterozygous women with other X-linked skin disorders.

Clinical features
Brown streaks and swirls become noticeable in the first year of life and may appear obvious by 2-3 years of age. The lines maybe light (hypopigmentary) or dark (hyperpigmentary). Associated findings (extra-cutaneous) that are not connected to skin may exist. Such findings may occur in the nervous system, musculoskeletal system or cardiovascular system.

Synonyms

 * Linear and whorled nevoid hypermelanosis
 * Reticulate hyperpigmentation of Iijima, Naito, and Uyeno
 * Zebra-like hyperpigmentation in whorls and streaks
 * Reticulate and zosteriform hyperpigmentation
 * Progressive cribriform and zosteriform hyperpigmentation.