Lichen nitidus https://en.wikipedia.org/wiki/Lichen_nitidus
Lichen nitidus is an inflammatory disease of unknown cause, characterized by 1–2 mm discrete, uniform, shiny, flat‑topped papules that are pale flesh‑colored or reddish‑brown. It most commonly affects children and young adults. Because lichen nitidus is generally asymptomatic, treatment is usually not needed.

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References Lichen Nitidus 31869173 
NIH
Lichen nitidus most commonly presents in children and young adults and does not favor one sex or race. Lichen nitidus presents as multiple, discrete, shiny, flat-topped, pale to skin-colored papules, 1 to 2 mm in diameter. These lesions commonly present on the limbs, abdomen, chest, and penile shaft. It is usually asymptomatic, so treatment is generally for symptomatic or cosmetically disturbing lesions.