Your skin barrier is not just a concept, it's an actual thing. And when it's been compromised, no serum, face oil, or mist can possibly work, or not work for long, at least. Before rushing out to try those hyped hydration hacks and products, take a step back and sort your surface. This guide is an introduction to a more thoughtful approach to your skin's health: prioritize the stratum corneum.

The uppermost layer of skin is referred to by dermatologists as the stratum corneum, and is based on a "brick and mortar" model. The "bricks" are corneocytes, flat, dead skin cells containing protein, which are stacked in a layer that overlaps with one another. The "mortar" is made from a lipid bilayer, made up mostly of ceramides, along with cholesterol and free fatty acids, which fills in the spaces between the cells and seals in the moisture.  Ceramides make up more than 50% of that mortar, by virtue of the way it is constructed. It is not an optional part of any product's formula. It is the most abundant structural component of the barrier. Reduce ceramide levels and the mortar falls apart. The water leaks out. The irritants get in. The game is over.  On top of all of this is the acid mantle, a fine, slightly acidic film made from the secretions of sebum, sweat, and biochemical residue. That's not there to look pretty. Its acidity is the trigger that handles the enzymes that break down the lipids and sequester the cells, and it also deters harmful bacteria and supports the skin's microbiome: the good bacteria that help defend skin against bad bugs. You mess up the acid mantle, and you are not merely dehydrating. You are essentially wrecking the entire biological defense unit that maintains your barrier. 

Skin that's dry and skin that's dehydrated, or has a damaged barrier, share some common symptoms, like that feeling of skin tightness and uncomfortable tautness. However, they're not the same thing. Dry skin is a skin type, a chronic condition that is likely influenced by genetics and how much oil your skin produces. Oily skin types can also have dry skin, since the cause is internal, but they could also just have oily skin that feels dry because of age or dehydration. A damaged barrier is an external condition and can happen to any skin type, including those with oily skin. If your skin stings or burns when you apply products that never gave you problems before, including things like toners, tap water, or products marketed as sensitive, your acid mantle may be compromised. Your skin feels tight, and also looks 'shiny' with no visible oil. Dry skin tends to look dull and feel rough, but an impaired barrier often looks tight and stretched, which causes products to just sit on top of the skin rather than sink in.  You're breaking out at the same time as all these other things. A healthy acid mantle (that protective barrier) keeps the bad stuff out, and when it's compromised, the bad stuff can get in, this includes the bacteria that causes acne. Your skin is just red, all the time, and nothing helps. This kind of redness indicates inflammation, which isn't always reactivity.  All of a sudden you can't deal with fabrics, sweat, or temperature changes. This may come first and show itself as an increasing sensitivity to very small irritants, which gives rise to contact dermatitis. If you have three or more of the above qualifiers, you likely aren't dealing with a lack of products. You need something to fix your skin, not hydrate it. 

There are differences between the moisturizers labeled "barrier repair" in what the proportions of ceramides, cholesterol, and free fatty acids are in their formulations. The proportion of 3:1:1 of ceramides to cholesterol to free fatty acids is a biological ratio identified by corneotherapy research as the most compatible with the necessary skin barrier lipid bilayer structure in order to restore the barrier. Moisturizers that rely only on ceramides or a single lipid variety can't replicate the structural complexity the skin absolutely requires to form a proper barrier. It has to be ceramides, cholesterol, and free fatty acids in around that proportion, or it doesn't work as well as it could. The most obvious example here is when you see a serum with ceramides in it, they can soften the skin but they can't shore up the barrier. This is why Sajic Skin Science formulations make use of a variety of ceramides, cholesterol derivatives, and phospholipids as well as shea butter and macadamia nut oil which are high in the kinds of free fatty acids known to be key components of the barrier. This is true biomimetic formula design. 

Too much exfoliation is the most common reason for a damaged skin barrier. Sadly, it's easy to do without noticing.  The effectiveness of products containing AHAs, BHAs, retinoids is appealing. Layering these products without considering their cumulative effect however can result in excessive exfoliation. For example, using a glycolic toner in the AM, a retinol serum in the PM, and a salicylic acid cleanser three times a week isn't three evenly divided treatments. It's a week of daily, continuous lipid degradation. Overly harsh surfactants also pose a problem. You know that squeaky-clean feeling that comes from a foaming wash? That's not oil removal; that's intercellular lipid removal from the skin surface. Using an indiscriminate surfactant when you have a thin but pristine oil layer means you're taking down all shield lipids rather than just the excess oil along with them. Low pH and high concentrations of popular exfoliants and other ingredients don't play well together. Vitamin C mixed with acidic ingredients amplifies the inflammation potential, prematurely activates granular enzymes on the skin cells, and can destabilize the vitamin C. Your skin ends up doing a great deal of babysitting instead of improving its own structure. 

TEWL, namely Transepidermal Water Loss, is the water's movement from the innermost layer of the skin through the epidermis layer and eventually out of the skin. This natural, passive process is regulated by a healthy stratum corneum. The lipid matrix in between corneocytes slows water movement and prevents excessive water loss. When this lipid matrix is degraded, which can be induced by factors such as UV-light, pollution, inflammaging but also chronological aging, this natural regulation fails, and water evaporates prematurely before cells have had the chance to complete their life cycle, leading to cell shrinkage. Smaller cells mean less space between them, which also results in impaired enzyme function and metabolic processes. When cells shrink, the cytoplasm retracts from the cell wall, pulling on the desmosomes that hold the cells together and causing the cells to gap. Not only do gaps in the cells let in potential irritants, but also UV radiation, all these can trigger even more inflammation.  To illustrate how important this is for signs of extrinsic aging: With time skin's natural ceramides decline, but so does enzyme activity in cell metabolism which decreases new ceramide formation. Secondly, smaller cells translate in releasing less natural moisturizing factors into the extracellular space. Finally, the more frequently smaller cells will "fall off" the body, the more sebaceous glands will respond with hyperproduction of sebum to form a new lipid matrix. You see now, that the process itself is already a downward spiral that multiplies because various feedback loops intensify each other. 

The more ceramides you lose over the years due to enzymatic decline and accelerated TEWL, the drier your skin becomes, the smaller your epidermal cells become, the less ceramides they produce, and the more frequently they are shed off your body, sending the sebaceous gland in overdrive creating a new lipid layer for which they lack the raw material. 

As if all this wasn't enough yet, the process of cell shrinkage releases damage-associated molecular patterns. These damage-associated molecular patterns act as danger signals that warn all surrounding cells that things have gone awry. Damaged cells die quickly and have to be replaced meaning you get through your allotted amount of cell division faster. That's why a malfunction in one cell soon leads to a cascade effect.  Those small cells not only excrete less extra cellular lipids, but they can't hold as many light-scattering keratin filaments in the tightly packed areas in between them as plump cells do. Smaller cells also reflect light differently transmitting the look of dull, dried out skin.  Affected skins do not only feel dry but because TEWL also takes away body heat from your skin and assists environmental substances to penetrate through your skin, your barrier function is impaired making you feel more severely any possible skin irritation.  Finally, smaller cells also mean more gaps between them. Your skin isn't watertight anymore. Perhaps, this goes a little too far, but hints in the development of Aquaporin by Beiersdorf obviously lies in this mechanism of how skin gets dehydrated because of accelerated extrinsic cell death through TEWL. Then there's the twofold negative effect because drying your skin further damages the remaining ceramides and natural moisturizing factors by rendering them ineffective. 

First, you need to stop the active destruction before you can rebuild. The corneotherapy borrowing approach often referred to as a skincare fast or elimination protocol, strip the routine to its minimum non-irritating components and stay there for a minimum of two to four weeks. 

1. A non-foaming, low-pH cleanser that removes surface debris without stripping lipids. Micellar water or gentle cream cleanser. Anything that foams hard, not.

2. A moisturizer fortified with physiological lipids ceramides, cholesterol, and free fatty acids rather than generic emollient blends. Your barrier can incorporate them, or be them, rather than having to metabolize or work around outside compounds.

3. A mineral sunscreen. UV exposure degrades ceramides and disrupts the acid mantle. It does this independently of any other damage present. Skipping this step slows healing. 

No actives. No vitamin C. No retinol. No exfoliating acids. Not for the duration of the fast. If the skin is burning when you apply a gentle cleanser it cannot simultaneously process ingredients designed to turnover cells faster. 

People want to know when they'll see results. The honest answer is: it depends on what part of the barrier you're talking about. Surface hydration, the squishy, dehydrated feeling, can improve within a week or so of consistent barrier-supportive moisturizing. It's not a perfect or comfortable solution, but it can make a noticeable difference when you go a week staying hydrated and appropriate moisturizer levels increase. Your skin will lose moisture slower, and your barrier won't be as quick to notice the hit. Structural repair takes longer. The skin cell turnover cycle, which is how long it takes new skin cells to travel from the basal layer of the epidermis to the surface of the skin, is about 28 to 45 days. For that amount of time, you need new lipids to be secreted by your living cells and picked up and processed by your dead skin cells to form a new, healthy barrier. That's the minimum timeline for meaningful restoration of the lipid bilayer and the acid mantle. This is also why people start building their barrier, see improvement after a week or two, and decide that must be good enough then start adding their active ingredients back in, only to have their skin sent back to square one in days. The skin looked better. The barrier wasn't restored. Forty-five days of a stripped-down routine feels long when you're used to a complex regimen. It's also the actual biology. There isn't a faster path that doesn't undercut the result. 

Once the barrier has been given that 28-day turnover cycle to restore and rebuild itself, we can start to look at introducing actives. How do you know what's an active? In our books, we'd class it as anything that isn't a basic cleanser, moisturizer, sunscreen, or antioxidant. So actives are ingredients like retinol, vitamin C, vitamin E, peptides, hyaluronic acid, niacinamide, and all sorts of various exfoliating acids (glycolic, lactic, salicylic). You have to approach them with caution. The last thing you want to do is damage your newly restored barrier all over again. So one at a time, as far apart from one another as you can. Do not introduce another active until the first one is being used with no irritation on maximum frequency.