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What is Beckers nevus and explain in detail?
Beckers nevus (also known as "Beckers melanosis", "Beckers pigmentary hamartoma", "nevoid melanosis", and "pigmented hairy epidermal nevus") is a benign skin disorder predominantly affecting males.: 687  The nevus can be present at birth, but more often shows up around puberty. It generally first appears as an irregular pigmentation (melanosis or hyperpigmentation) on the torso or upper arm (though other areas of the  body can be affected), and gradually enlarges irregularly, becoming thickened and often hairy (hypertrichosis).  The nevus is due to an overgrowth of the epidermis, pigment cells (melanocytes), and hair follicles. This form of nevus was first documented in 1948 by American dermatologist Samuel William Becker (1894–1964).

Clinical information
Medical knowledge and documentation of this disorder is poor, likely due to a combination of factors including recent discovery, low prevalence, and the more or less aesthetic nature of the effects of the skin disorder.  Thus the pathophysiology of Beckers nevus remains unclear.  While it is generally considered an acquired rather than congenital disorder, there exists at least one case report documenting what researchers claim is a congenital Beckers nevus with genetic association: a 16-month-old boy with a hyperpigmented lesion on his right shoulder whose father has a similar lesion on his right shoulder.

Prevalence
The most extensive study to date, a 1981 survey of nearly 20,000 French males aged 17 to 26, served to disprove many commonly held beliefs about the disorder