Skin is everywhere. When it's not on you, it's sloughing off you. I've heard that dead skin accounts for most of the dust in our homes.
Actually, skin isn't on you, it is you. As you may have learned in school, skin is the largest organ of your body. As the popular aphorism "beauty is only skin deep" implies, without your skin you would not look good.
But that doesn't mean we're all comfortable in our own skins. You may be thin-skinned, as I am, about almost any criticism—of my cooking, my singing, my writing, my skin itself. You could say I'm thin-skinned about my thin skin.
Even if you're thick-skinned and hence able to withstand the slings and arrows of your worst enemies, eventually something will get under your skin and really annoy you. This blog, perhaps.
I could take this opportunity to riff on dermatologists or rail about moles, rashes, wrinkles, and other indignities that afflict the skin, but I think I'll end here and escape by the skin of my teeth.