Blaschko lines

The pattern assumed by many different naevoid and acquired skin diseases on the human skin and mucosae. The cause of the pattern of Blaschko lines is unknown; they do not follow nerves, vessels, or lymphatics. In 1901, on the occasion of the 7th Congress of the German Dermatological Society held in Breslau, Blaschko presented his observations on various linear dermatoses. He pointed out that the lines described by these conditions did not only not correspond to any known anatomical basis, but were remarkably consistent both from patient to patient and even from one disease to another. Blaschko proposed an embryonic origin for these lines, but did not elaborate. The lines may represent a clinical expression of a genetically programmed clone of altered cells, perhaps first expressed during embryogenesis