English reaches for 'skin' through a Norse word for what is cut from a carcass — the pelt, the remove — and Spanish finds 'piel' in Latin's pellis, which named the fleece pulled from an animal's back; in both, the self arrives through the metaphor of something that could, in principle, come off. Chinese thinks more carefully: 皮肤 pairs the sign of a hand mid-flay (皮) with the character for the body's own membrane (肤), as though the language noticed that skin-as-peel and skin-as-self are not quite the same thing. Esperanto's haŭto, drawn from German Haut by Zamenhof in 1887, traces to the PIE root that also fathered Latin cutis — the clinical word doctors still prefer — suggesting that a planned language, when forced to choose, reached for the scientific rather than the visceral. What all four share, finally, is the awareness that skin is a threshold: every word here carries the ghost of its own crossing.
Old English relied on 'hȳd' (hide) for the same concept; 'skin' entered Middle English from Old Norse through Viking trade contact and gradually displaced the native word for the body's outer surface. The deeper PIE root is contested.
Spanish also inherits 'cutis' (from Latin cutis, from PIE *[s]kewH- 'to cover') for facial skin or complexion, and 'dermis' in medical register — two additional strata revealing different layers of Latin inheritance, each from a separate PIE root.
An oracle-bone pictograph of a hand at the moment of flaying — the Shuowen Jiezi confirms it: 'the form represents a hand holding skin.' Skin defined not as a surface to inhabit but as the thing in the act of being removed.
The flesh radical 月 (abbreviated from 肉) anchors the character in the domain of the body; 孚 contributes sound rather than sense. This is the inhabited side of the hide — the skin as self, not as pelt. Attested in the Shijing simile '肤如凝脂' (skin like congealed lard), the classical measure of beauty.
皮 alone ranges across fruit peel, animal hide, leather, rubber, and human skin. 肤 is nearly always specifically the skin of a human body as organ. Together, 皮肤 specifies the dermal layer — what anatomy means when it says 'skin.'
A root word with no productive Esperanto affixes to decompose. Zamenhof derived it from German 'Haut,' which traces to Proto-Germanic *hūdiz and PIE *[s]kewH- 'to cover, conceal' — the same root that yielded Latin 'cutis' (whence English 'cutaneous') and, separately, English 'hide' (the noun for animal skin). This makes haŭto etymologically closer to Spanish 'cutis' than to English 'skin,' a fact the surface forms entirely conceal.
Every language named the body's outermost edge by first imagining what it would mean to remove it.