Brick-mortar model of the barrier
The stratum corneum, the outermost layer of the skin, consists of dead keratinocytes (corneocytes) and the lipid matrix between them. If we compare this to a wall; corneocytes are the bricks, and lipids (ceramide 50%, cholesterol 25%, free fatty acid 15%) are the mortar. When the mortar deteriorates, the wall loses its function. This is measured as an increase in Transepidermal Water Loss (TEWL) and leads to complaints such as dryness, redness, and sensitivity of the skin.
Skin microbiome: an ecosystem that knows how to survive
Approximately 1 trillion bacteria, fungi, and viruses live on your skin. These microorganisms are not harmful; most are beneficial or neutral. "Good" bacteria like Staphylococcus epidermidis keep the skin's pH acidic (4.5-5.5), preventing pathogens from adhering. Although Cutibacterium acnes is the classic culprit in acne patients, it is actually a beneficial bacterium found in healthy skin; it causes problems when its balance is disturbed.
The more diverse the microbiome, the more resilient the skin. Excessive soap, alcoholic toners, and frequent peeling reduce microbiome diversity — making the skin "sterile." Sterile skin is not strong skin; on the contrary, it is an overly reactive skin.
Barrier in HEALTHY skin
- TEWL (water loss) low
- pH acidic between 4.8-5.5
- High microbiome diversity
- Low inflammation level
- Tolerant to active products
Barrier in DAMAGED skin
- TEWL high — skin "dehydrated"
- pH shifted towards alkaline 6+
- Reduced microbiome diversity
- Low-level chronic inflammation
- Tingling, redness to products
Common mistakes that damage the barrier
My observation in daily skincare is this: patients don't come saying "they don't do enough skincare"; they don't realize "they do too much." Peeling twice a day, three different acids, a lightly abrasive cleansing brush, alcoholic toner, and a hardened steel mask on the weekend. When I listen to this agenda, I find sensitivity, redness, or a finely flaky surface on the patient's skin.
Barrier treatment is interestingly done with "less." 50-70% of actives are removed for a while, and repairing creams containing ceramides and cholesterol are added. Usually, the barrier recovers within 4-6 weeks, and the skin responds to proper care again.
Clinical note:In 80% of rosacea patients, the initial treatment is "to stop what is being done." Not to add a new product, but to remove the damaging ones. This is the fundamental lesson of barrier medicine.