Abstract
Blaschko''s lines are the pattern assumed by many different nevoid and acquired skin diseases on the human skin and mucosae. They were described and drawn by Blaschko 75 yr ago. These lines are to be distinguished from other linear patterns such as Voight''s lines, Langer''s lines and the lines of innervation of the spinal nerves. They do not follow any known nervous, vascular or lymphatic structures in the skin. The epidermis and its appendageal structures, the melanocytes, the vascular system and the fatty hypoderm, all, separately or in combination, may be involved in the morphological manifestations which follow Blaschko''s lines. Many of the nevoid skin conditions are lifelong (e.g., linear sebaceous nevus, unilateral nevoid telangiectasia); many of the acquired skin diseases (e.g., lichen striatus, linear psoriasis) are of relatively short duration (e.g., 1-2 yr). The cause of the distribution pattern is unknown. It is possibly a form of human mosaicism where certain specific cells or groups of cells react differently from other cells due to chromosomal abnormalities. The embryological explanation of Blaschko''s lines is not at all clear. Other markers in addition to the skin findings are needed to determine the time and the nature of the change responsible for these lines. [Possible chromosomal and embryological abnormalities need further study as to their linkage to the lines.].

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