Sensitivity

Sensitive skin is not a single condition but a phenotype produced by three converging mechanisms. Each operates through measurable biological pathways and each responds to specific dermocosmetic interventions. Patients who are told their sensitivity is psychosomatic are usually patients whose mechanisms have not been mapped. The three pathways below sit on decades of published evidence and explain why a calm, minimal routine outperforms an aggressive corrective one.

Skin barrier function and TEWL

The stratum corneum is the body's primary water-retention layer. Its corneocyte-lipid bilayer — a brick-and-mortar architecture of dead keratinocytes embedded in ceramides, cholesterol, and free fatty acids — controls how much water the skin loses to the environment. Transepidermal water loss (TEWL), measured in grams per square metre per hour, is the standard biophysical marker of barrier integrity. Healthy skin sits around 5–10 g/m²/h; sensitive and reactive skin commonly measures 12–25 g/m²/h or higher.

When the barrier thins, two problems compound. Water loss accelerates, leading to tightness, dullness, and flaking. And the lipid mortar that normally blocks irritants from reaching nerve endings becomes permeable, so substances that healthy skin tolerates without notice — surfactants, low-molecular-weight fragrance, ethanol — penetrate to depths where they trigger neurosensory firing. Barrier-rebuilding actives address this directly: 3:1:1 ratio of ceramides, cholesterol, and palmitic acid restores the physiological mortar; niacinamide upregulates filaggrin synthesis; squalane fills lipid voids while the barrier rebuilds. The intervention is structural rather than symptomatic.

Neurosensory reactivity (TRPV1, capsaicin pathway)

The TRPV1 receptor — discovered by Caterina and colleagues in 1997 — is a calcium ion channel expressed on sensory nerve endings in the dermis. It opens in response to heat above 43°C, capsaicin from chili, and certain low-pH cosmetic actives, transmitting the stinging-burning signal that defines sensitive skin. In the reactive phenotype, TRPV1 is upregulated and primed: it fires at temperatures and concentrations that healthy skin ignores. The result is that visible inflammation is not required for symptoms — patients can experience persistent stinging from a product that produces no measurable redness.

TRPV1-modulating actives reduce this reactivity through different mechanisms. Centella asiatica extract downregulates TRPV1 expression over four to eight weeks of consistent use; ectoin stabilises membrane proteins and dampens neuronal signalling; allantoin and beta-glucan reduce sensory nerve sensitivity at the dermal interface. None of these actives produce overnight relief — sensory nerve thresholds reset slowly — but at the eight-week mark patients describe a measurable reduction in subjective stinging and tolerance for previously off-limits ingredients. This is why sensitive-skin care fails when measured at two weeks and succeeds when measured at twelve.

Inflammation and the inflammaging cycle

Chronic low-grade inflammation is the third mechanism and the one most often missed. When the barrier is compromised and TRPV1 is firing repeatedly, local immune cells — keratinocytes, mast cells, and Langerhans cells — release pro-inflammatory cytokines including IL-1, IL-6, and TNF-alpha. These cytokines have a paradoxical effect: they slow lipid synthesis in the stratum corneum, further compromising the barrier that allowed them to mobilise in the first place. The cycle is self-reinforcing.

Dermatologists describe this loop as inflammaging — chronic, low-grade inflammation that progressively ages and weakens reactive skin. The clinical correction has three steps. First, remove the input — every irritant in the routine, however mild it seems. Second, restore the barrier with ceramide-rich moisturiser applied twice daily. Third, add redness-soothing actives that calm the cytokine signal — Niacinamide, Panthenol, Madecassoside, and Zinc PCA each have published evidence for reducing redness and easing reactivity over four to twelve weeks. The full Sensimed routine is engineered for exactly this sequence and avoids fragrance, ethanol, essential oils, and high-strength acids that would restart the loop.