Recently, I've seen a lot of articles, Youtube videos and even ads on "moisture barrier." (Way to go, Jennifer Aniston) It's exciting that more and more people understand the importance of keeping a healthy barrier. The more people are aware of it, the more people will have healthy skin, yay! We've briefly talked about repairing the barrier in a previous post, but I think it is also essential to understand how the barrier repairs itself so we know how to support and maintain it.
I already sound like a broken record, but the moisture barrier is mainly composed of barrier lipids (Ceramides, Cholesterol and Fatty acids). These lipids act as waterproof cement in between your corneocytes (dead skin cells). When your skin encounters damage (too much sun exposure, harsh surfactants, mechanical damage, etc.), your barrier lipids get depleted, leaving your skin dry and exposed to more damage. But luckily, your skin has a way to repair itself.
Skin Composition Recap
Your SG cells are responsible for producing the barrier lipids. They secrete them in the form of lamellar bodies, which are sac-like bags filled with layers of unprocessed barrier lipids. Although lamellar body secretion is primarily constant, your cells also have a reserve of pre-formed lamellar bodies just in case it needs to repair itself. Think of them as barrier bombs.
Tight Junctions are unique structures in your SG that restrict water and solute movement to the upper layers of your skin. One of these critical solutes is Ca2+ ions, which serve as a signal for many skin processes. In healthy skin, Ca2+ ions are restricted by the Tight Junctions leading to higher extracellular Ca2+ concentrations in the SG.
Timeline of Barrier Repair
The moment of truth. You got fully vaccinated and flew to the Maldives. You were so excited to plunge in the water that you forgot to wear sunscreen (audible gaspp!!!!). You were lying there exposed when it hits you that you forgot to wear sunscreen! (Dun dun dun...). And so the clock begins
T= 0-3 minutes
Time 0 starts when Barrier Damage happens. Barrier damage is usually characterized by loss of your barrier lipids, destruction of your Tight Junctions, and the release of your inflammatory messengers (another super exciting topic). One thing to note is that barrier damage constantly happens in different regions of your skin. It just becomes more apparent when a large area of your skin is affected, and enough amplification of the inflammation cascade happens. This is when you see redness, tightness, dryness and scaliness.
When your Tight Junctions dislocate, the Ca2+ rushes out of the SG border and distributes itself throughout the upper layers of the skin. This decrease in extracellular Ca2+ ions in the SG, signals your cells to repair themselves. Once this signal happens, your SG cells start secreting their pre-formed pool of lamellar bodies, which becomes the unprocessed barrier lipids in the upper layers of your skin. The cells keep secreting these lamellar bodies, and by 3 minutes, they won't have any lamellar bodies left inside them.
T= 3 to 30 minutes
The secreted barrier lipids spring out into a fence-like barrier in the upper layers of the skin. They offer some protection, but because they are not processed yet, they are not yet connected and are not fully waterproof. What's interesting here is that the ceramides are released alongside the enzymes needed for their processing.
You might ask: But if the ceramides are packaged with their enzymes, why aren't they processed yet when they get released?
The reason is that these processing enzymes are pH-regulated divas. They can't start processing unless they reach the level in the skin where the pH matches the pH that they want. So at this moment, your skin has some protection but not quite.
T= 30 min to 6 hours
By this time, your cells would start producing Cholesterol and Fatty acid. Shortly after, Ceramide production increases, and these three will start getting packaged into new lamellar bodies. Secretion of these new lamellar bodies is increased, and by three to six hours, your SG cells have fully replenished their lamellar body content.
Ceramides that are released are in the form of Glycosylceramide and Sphingomyelin. As mentioned above, the processing enzymes (B-glucocerebrosidase and Sphingomyelinase) both need an acidic pH of about 5.5 for them to work. As they reach the acidic upper layers of the skin, they become more active. B-glucocerebrosidase cleaves Glycosylceramides into Glucose and various Ceramides, making Ceramide more hydrophobic. Sphingomyelinase processes Sphingomyelin into Ceramide AS and Ceramide NS.
The important thing to note here is that these Ceramide Processing Enzymes are pH-dependent, underlining pH's importance in barrier repair. Skin pH also increases when the skin gets damaged. Due to the alkaline pH, these two enzymes won't work as well in processing Ceramide. If your skin remains alkaline, these enzymes not only lose their activity but also get degraded over time. This highlights the need to be mindful of pH in your routine. Make sure to know when to apply products with different pHs.
At this time, DNA synthesis increases, and the cells in the SG starts repairing themselves. The Tight Junctions reappear, and control of Ca2+ ions is re-established. The cells detect the increase in extracellular Ca2+, decreasing the release of lamellar bodies, which signals restoration to normal.
This is how the skin repairs itself. However, this is not a perfect process, and almost always, something in the process goes haywire. In the next series of articles, we'll discuss the potential steps in the process where it can go wrong and what we can do to help your skin repair itself.