STRETCHED OVER a singular arrangement of muscle, bone, and memory, skin is the membrane that distinguishes self from world. Inside its margins: you. Beyond its flexy surface: everything else. Pause to consider this for long, and you may be inclined to sit very, very still. To call attention to yourself seems risky, even insane. There should be more than this flimsy dermal bubble separating the vastness of the cosmos from the throb of blood and consciousness that is you.

Your skin marks the tangible, visible, and sensory edge of the anatomical landscape you claim as your own. From fingerprints to facial features, the thin topcoat of your body carries the nuances of form, texture, and tone that make you identifiable as an individual. Think about the variability of your skin, the medley of textures that play across your body’s convolutions: smooth, lined, shiny, baggy, tight, freckled, scarred, goose-pimply, plump. Here, skin hugs the rim of a nostril. There, it throws a seductive curl over the tragus of the ear. It cups your heels with thickened pads. On your knuckles, creases coalesce like knots on a pine board.

Your skin’s position at the body’s outer edge obligates it with protective functions. It guards the tender tissues of your interior from heat, cold, pathogens, and the sharp edges of the world. But to be alive — to be human — you must let certain things in. Lest you explode from the weight of your waste, loneliness, and bad ideas, you must also let some things out. Your skin, accordingly, is shot with holes — pores, nostrils, auditory canals, ducts, the ins and outs of the digestive tract, sockets for eyes.

Skin is the edge to which nerves run their finest feelers. What you register at your body’s fringe is the dazzling sensory display that we corral under the term “touch”: the sloppy glide of a dog’s tongue, the sharp ache of snow trapped between wrist and mitten cuff, the scabrous rub of sand beneath your feet, the spark of pain when you bang your shin on the lowered door of the dishwasher, cool fingers on a fevered forehead, a kiss. At its best, sensation is a shared gift, touch and feel echoing and bouncing between bodies.

Over most of the body, the structures that house the peripheral nerves are arranged in a uniform carpet of bumps, like the taste buds scattered across your tongue. At the body’s extremities, however, a more refined sense of touch is called for. The meandering ridges and furrows that grace your palms and soles show where touch receptors are packed together as tightly and efficiently as possible. These fluid patterns of whorls, arches, and loops are popularly called fingerprints, but they also swirl across the soles of your feet and are more formally referred to as “dermatoglyphics,” from the Greek roots derma and glyphein: skin carving. Your dermatoglyphics reflect a biological investment in heightened sensitivity where you most commonly make contact with the world.

It is convenient to think of the human birthday suit as a membrane that separates, preserving the boundary between self and not-self. But from the moment your parental gametes linked their half-strands of DNA to form the zygote that would develop into you, everything you now claim as yourself has been derived from matter and information imported across your body’s external membrane. The world may be full of things that slash, nibble, pierce, abrade, infect, and sear, but it is also replete with oxygen, sunlight, chocolate, laughter, the colors of leaves in autumn, the smell of fresh-baked bread, the twining of bodies under the covers on a winter’s night. Skin differentiates but does not isolate. Your singular existence unfolds within it, but skin does not hold the universe at bay. Instead it marks the seam that joins your existence to everything else.