We often forget about our skin when all is well. We all zero in on the skin when things are NOT going well, but in this article, we look at the magic that happens under the visible part of the skin which helps keep you safe, healthy, and beautiful, and what you can do to keep it that way.
The human skin is incredibly complex. Not long ago, the skin was viewed as something like a piece of leather, just a boring material that covers the important organs underneath. Over the last several decades, we’ve really started to increase our understanding of the various biological processes that occur and have gained an appreciation for the various ways in which the skin protects us. The skin doesn’t just look pretty (when it does). It’s constantly working hard to protect you in various ways, completely out of your sight. The skin serves us in at least 4 important ways:
Physical protection: At its simplest, the skin forms a basic wall – what we think of when we think of skin – something that comes between the organs and anything that the outside world might throw at you. There are many subtle complexities even in this basic function, however. In addition to blocking out much of the impact from the dodgeball that’s thrown at you, it also needs to block out potentially harmful bacteria, viruses, and fungi, that you are constantly exposed to. The skin also regulates proper moisture levels so that your body doesn’t just turn to mush when you take the next shower or evaporate when you go outside in a dry climate. In fact, common skin conditions like eczema largely have to do with a problem in this barrier function – the skin’s ability to regulate moisture levels properly.
The skin that is visible at the top is actually dead skin, soon to be chaffed off and replaced by newer skin that pushes the old skin out of the way. Called the skin cycle, it takes about 28 days for the skin cells to push up from the bottom of the epidermis to the top and become replaced.1 The physical barrier is often compared to brick and mortar; the skin is composed of a sandwich between hard cells called corneocytes (the brick) and are held together by intercellular lipids (the mortar that holds it together) that are a combination of ceramides and free fatty acids. It takes just the right combination and composition to have healthy skin that is supple and healthy, and when this is disrupted, we see things like eczema, dull skin, or easily irritated or inflamed skin.
Thermoregulation: The human body is quite delicate and extremely sensitive to temperature changes. Even a few degrees of change in internal temperature, either up or down, can constitute a medical emergency. We start to sweat almost as soon as our outer body temperature hits 37 degrees. On the other hand, we form goosebumps on our skin and shiver when it gets cold. Humans are incredibly adaptable, living in almost all climates on earth due in large part due to our ability to regulate our internal temperatures so effectively and precisely. The skin plays a major role in regulating this fine balance.
Sweat glands are located in the dermis, just below the thin epidermis, allowing sweat to be expelled up to the surface. Although most of us hate it, and some of us purchase products like antiperspirants to manage excess sweat, it’s a critical function that allows us to use evaporative cooling to keep ourselves from overheating.
Immune function: The immune system starts right at the skin – and it makes sense considering that the skin is constantly being exposed to various antigens (virus, fungi, bacteria). Inflammation, which we all despise, is actually an important first-line defense of the immune system and is triggered by various skin mechanisms, some of which we don’t completely understand yet. Also, many skin conditions like psoriasis have to do with a problem within the skin’s immune functions.
Langerhans cells are present at the epidermis and act as a police force to present potential antigens to the immune system. Cells called macrophages clean up various antigens, as well as dead or dying skin cells. They also work with T-cells so that they can produce specific antibodies to the antigen.
Protection from UV light: UV damage is one of the most common sources of environmental damage. The sun has been a thing before all life on earth, and we, like other living organisms, have found a way to survive under sunlight. Humans produce a pigment called melanin (producing a tan) from melanocytes which reside in the skin. Melanin provides the color in human skin. It also scatters light from the sun, protecting from UV light that the sun radiates, which can cause cancer and skin deterioration.2 People living closer to the equator tend to have darker skin, likely due to this adaptive response. Melanin is our skin’s natural first line of defense against UV light. It’s estimated that tan might confer something like SPF4. Not a ton of protection, but it’s the body’s way of trying to mitigate further injury from future exposure. It’s important to know that just because it’s a “natural” protection that it’s sufficient; a more accurate way of viewing tan is that this is evidence of sun damage.
The skin isn’t just a piece of leather. The skin is an intelligent organ that has multilayered defenses that help protect our bodies from fungi, viruses, bacteria, UV radiation, heat, cold, and of course, physical impact. It’s easy to feel frustration at the skin’s imperfections – a bump here, a scar there, a blotch, a wrinkle, an itchy spot, sweat, and so on. Indeed, all we ever do is complain, but it can be helpful and calming to remind yourself from time to time that your skin is always working hard to keep the bad guys out. Treat your skin well; it does a lot for you.
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1The visible skin is actually composed of dead skin cells. In psoriasis, the plaques occur due to this process working too quickly at around 14 days or so, causing the skin to be premature at the surface due to inflammation.
2As we’ve mentioned several times already on DermLetter, the protection that melanin provides is limited and does not mean that you can stay in the sun forever.