How Does the Skin Barrier Work?

incredibly effective armor built to fend off specific attacks. It's not great at handling swords or arrows, but to be fair, those are relatively new inventions, far older threats like microbes and ultraviolet light. That's where our skin is a hero. It's our first line of defense as we move through the world, though it operates more like the manned walls

of a castle than armor on a knight. Specialized cells and surrounding structures form a physical barrier between you and everything that's not you, sort of like a castle wall, and inside of that, an immune barrier stands at the ready like a castle's guard, to eliminate any threats that do make it through. But for our body's most visible organ. All of this happens on a microscopic level. So today let's delve into the skin barrier, how it protects us,

and what can happen when something goes wrong. We've talked before on the show about the layers of the skin. The innermost layer, the hypodermis, provides structural support. It contains fat to insulate and cushion our underlying muscles and organs, plus blood vessels to get supplies to the middle layer, the dermis. The dermis contains all of the skin's equipment, nerve endings, sweat glands, pair follicles, and so on. All of that is sealed in and protected the outermost layer,

the epidermis. The epidermis itself has two main layers, the inner of which is living, and the outer of which is dead. The dead skin cells of the outer layer are what we see and touch, and it's called the stratum cornium. The stratum corneum is often described as being like a brick wall, though luckily for us, a very flexible one, because it's made up of tough cells that are stacked and bound together with a kind of mortar of waxy, fatty lipids and some adhesive proteins. Those tough

cells are called corneocytes. It's weird to think that their entire purpose in life is to die, but it's for the greater good of the organism. Because they're dead, they can't be infected by a virus or stopped from doing their job by bacteria. At their job is to sit there. They develop in the inner part of the epidermis, and as they're pushed to the out side, they die and flatten into sort of long, hardened envelopes containing keratin. Keratin is the protein that makes our hair and nails tough,

and other things too, like feathers, hoofs, and horns. The etymology of the words keratin and corneocyte is actually related to the word horn. They all root back to early Indo European words for the hard and bony things that come off of an animal's skull. It's the same root where we get the word for the horn shaped cornucopia. Anyway, the tough corneocytes in your stratum corneum also contains stuff that can grab up molecules of water, which is good

because ideally your outer skin should be dry. No one wants permanently moist skin, but not too dry. Having a bit of water in your skin keeps it pliable and prevents the skin from cracking. And as I said, the corneocytes are bound together with the sort of mortar made up of sticky proteins and a bunch of lipids, which are fatty or waxy substances. This is great because a it holds the corneosytes tightly in place, and also b

it's what makes our skin more or less waterproof. Oil and water repel each other, so the oily lipids help make our skin impermeable to water. The stratum cornium is essentially the reason that all of the water that makes up some sixty percent of our body and makes our organs work stays in our body and doesn't just evaporate out. It also prevents many potentially harmful water based liquids, including

ones that contain germs, from leaking into our body. Not too shabby for a stack of dead cells only some ten to twenty micrometers thick, which is about the thickness of one or two layers of plastic wrap. Even the fact that the corneocytes are dead and thus can't be repaired when they wear out and therefore get sloughed off and replaced on a continual basis. That's a feature, not a bug. This way, any microbes that might take up residents in or around your corneocytes get slothed right off

with them. In healthy skin, your stratum cornium totally replaces itself about once a month. The cells in the layer of the epidermis directly beneath the stratum cornium where the corneocytes develop, are also tightly junctured together, adding to the security of the physical barrier of our skin. Plus they release some helpfully antimicrobial molecules. Because as impressive as this physical barrier is, it is then and delicate and pretty

easily scratched or pierced. That's why we have an immune border guard lying in wait just inside our skin's castle wall. Our immune system is really complicated, and I am not a medical professional, y'all, I was an English major. But very basically, your epidermis and dermis each contain some specialized immune cells that can contain and neutralize any invaders. They can also call in backup from other immune cells that exist throughout the body via chemical signaling that creates inflammation.

If you think about the last time you got a scrape or a cut, you may have noticed that it got reddish or purplish and puffed up a bit. That inflammation may be uncomfortable, but it's our body's way of getting extra supplies to the site of an injury to prevent infection and heal everything up. Once that backup arrives to the site, all of the immune cells work together inside the skin to clear out invaders and cellular debris. When they're done, other cells call off the inflammation and

everything goes back to normal. The physical barrier is restored, and the immune barrier steps down from red alert to a state of watchful preparedness. Of course, this is assuming that everything is operating normally. The creation of the physical barrier and the responses of the immune barrier are both extremely complex processes, and unfortunately, any number of things can upset them, either from the outside in or the inside out,

or both. Just for example, that lipid mortar around corneocytes gets produced by the corneocytes themselves as they develop into their final form. So if anything changes in the cells developmental process, say if it moves too fast, that doesn't just disrupt how those corneocyte bricks stack up. It can also disrupt the formation of the mortar around them, and having too much or too little of any component in the bricks or the mortar changes the way that the

wall holds together. From the outside, our skin can become brittle if our environment is too dry, but it can also get flaky if it's too humid. Exposure to irritating or allergenic substances can cause an overactive immune response. Getting too much sun does cellular damage that your skin has to repair, which when repeated, will reduce cellular function over time.

Even our mental health and stress levels are tied into how our organs function, and our skin certainly is an exempt, as anyone who's ever gotten a ZiT before a big event can tell you. From the inside, there are a number of diseases and conditions that muck about with some part of the skin barrier's upkeep, resulting in itchiness, flakiness,

or other discomfort at best. For example, we talked recently on the show about psoriasis, a condition in which a combination of skin cell overgrowth and immune system freak out creates uncomfortable, scaly, or discolored patches that come and go, triggered by those outside stressors that I mentioned. If you or someone in your care experiences chronic skin barrier disruptions that result in that kind of issue. Definitely talk to a medical professional about the best way or ways to proceed.

There are lots of topical and systemic treatments that can help control activity in the immune system or the skin, and a healthcare provider will be able to help you with the diagnosis and a plan. That being said, even finding a regimen that keeps quote unquote normal skin happy can be a challenge because the skin barrier is so complex that its exact functions are really pretty unique to

all of us, and it changes over time. Simply getting older means that our skin structure thins and becomes less elastic and develops a different balance of immune cells. These changes in our skin barrier make us more susceptible to infections.

A specialist like a dermatologist or esthetician may be able to help find exactly the right kind of moisturizer and other products for you, but the top level advice is to prevent skin barrier damage in the first place by treating your skin gently, protect it if you're going to be handling harsh chemicals or going out in the sun, and don't over cleanse after all, if your skin is your castle, your first duty is to respect such a grand structure. Today's episode is an original written by me.

Brain Stuff is production of iHeartRadio, produced by Tyler Klang. Four more podcasts my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.