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liver spot
Liver spots (also known as age spot, solar lentigo,〔 "Lentigo senilis", "Old age spot,"〔 "Senile freckle") are blemishes on the skin associated with aging and exposure to ultraviolet radiation from the sun. They range in color from light brown to red or black and are located in areas most often exposed to the sun, particularly the hands, face, shoulders, arms and forehead, and the scalp if bald.
The spots derive their name from the fact that they were once incorrectly believed to be caused by liver problems, but they are physiologically unrelated to the liver, save for a similar color.〔Karen J. Carlson, Stephanie A. Eisenstat, Terra Diane Ziporyn, ''The new Harvard guide to women's health'', Harvard University Press, 2004, p.337.〕 From the age of 40 onward the skin is less able to regenerate from sun exposure, and liver spots are very common in this age group, particularly in those who spend time in the sun.
In the overwhelming majority of cases, liver spots pose no threat and require no treatment, though they occasionally have been known to obscure the detection of skin cancer. However, despite being a benign condition, liver spots are sometimes considered unsightly and some people choose to have them removed. This can be done by electrosurgery, laser treatment, cryotherapy, or the use of tretinoin or alpha hydroxy acids.〔(【引用サイトリンク】url=http://www.beautynaturalskin.com/overview-about-liver-spots/ )〕
== Causes ==
Differently from the melanotic nevi and the verrucous nevi on the skin, age spots change with time in color and in shape. Misrepair-accumulation aging theory proposes a hypothesis on the development of age spots. Firstly, the development of a flat spot is a result of accumulation of aged basal cells. When the skin is aged, some aged cells that contain lipofuscin bodies cannot be removed. An aged cell will affect the functionality of the local tissue and promote the aging of its neighbor cells. By a feedback loop, more and more neighbor cells become aged and lipofuscin-containing. They aggregate and form a spot with irregular shape. Secondly, protruding of a flat spot is a result of death of aged cells in the spot and release of lipofuscin bodies. Isolation of the un-digestible lipofuscin bodies in a fibrotic capsule is essential for maintaining the structural integrity of the tissue. Successive encapsulation of dead cells and lipofuscin bodies results in the growth of a spot in three dimensions. The dense lipofuscin bodies in the capsule make a protruding spot soft and dark in color.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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