Skin
The skin barrier only works in an acidic environment
14 September 2026
“Damaged barrier” sounds like a metaphor. It is not. The epidermal barrier is a physical structure: corneocytes stacked like bricks, and between them a mortar of lipids arranged in multilayered sheets — ceramides, cholesterol and free fatty acids in tightly set ratios.
That mortar is not poured in ready-made. It is built on site, in a narrow intercellular space, by an enzymatic reaction.
Enzymes have a pH optimum, and it is not negotiable
Lipid precursors are ejected from cells in lamellar bodies: glucosylceramides and sphingomyelin. To become ceramides able to build a tight structure, two enzymes must act — beta-glucocerebrosidase and acid sphingomyelinase. Both work best in an acidic environment, around pH 5.5.
Raise pH to 7 and those enzymes slow down. Lipids stay in precursor form. Lamellar sheets pack incorrectly — looser, less ordered. Water escapes faster through a barrier built that way (TEWL rises), and irritants enter more easily.
The second front: excess shedding
In parallel, the opposite happens. Kallikreins — proteases that cut the links between corneocytes — have their optimum in alkaline pH. In an alkaline environment they work overtime and loosen the stratum corneum faster than they should.
Net effect: less lipid mortar and weaker cell-to-cell links. The barrier weakens from both sides at once.
How it looks in the mirror
Tightness right after washing. Roughness. Redness that was not there before. Stinging from a product that used to feel neutral. Skin that is oily and flaking at the same time. Formulas that “suddenly stopped working”.
That is not an allergy to one ingredient. It is a barrier that has stopped holding.
Repair starts by removing the load
Barrier recovery does not first require adding something. It requires stopping the damage. The order that works:
- 1.Swap soap and harsh detergents for a cleanser with acidic pH and mild surfactants.
- 2.Reduce acids and retinoids for 2–3 weeks. Not forever — for the healing window.
- 3.Supply what is missing: ceramides, cholesterol, fatty acids, plus humectants that bind water (glycerin, PCA, urea).
- 4.Drop physical exfoliation and hot water.
First changes are usually visible after 2–3 weeks. Full stratum corneum turnover takes about 28 days and lengthens with age.