We have skin that covers our bodies but when does it stop being skin? Our tongues have skin but do our throats? What about our stomachs, lungs, intestines, and everything on the inside they don’t have skin. So where does it end and become whatever it is?
In: Biology
Everything in your body should have an epithelium (basically an outer layer of sorts) and a membrane that creates that particular organ “space” with in your body IE : the pleura for your lungs or the meningeal layers that protect your brain, there’s even the periosteum that covers your bones hell even the skin itself has an epidermis.
On to your question the skin is an organ that functions as the outermost layer of what is you (among other stuff) therefore only the outer layer of you is skin like the palm of your hands or your face when on the inside say your mouth that outer layer within you is not skin just another epithelium , the tongue for example has an stratified epithelium.
Edit some sources : [on the skin](https://www.ncbi.nlm.nih.gov/books/NBK537325/) and [epithelium](http://www.histologyguide.com/slidebox/02-epithelium.html)
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