Creative Touch Permanent Makeup and Aesthetics

Desquamation is not passive shedding – it is a precisely timed enzymatic programme that removes approximately 30,000–40,000 corneocytes per hour whilst maintaining constant stratum corneum thickness. The serine protease KLK5 cleaves corneodesmosomal proteins (desmoglein 1, desmocollin 1, corneodesmosin) to release corneocytes at the surface. Its inhibitor LEKTI binds tightly to KLK5 at the acidic pH of the lower and mid-SC, then dissociates as corneocytes reach the near-neutral surface – using the acid mantle pH gradient as a spatial release timer. Alkaline pH, hard water mineral deposits, and inflammatory KLK5 overexpression each disrupt this timer differently: producing retention and roughness, premature shedding and barrier loss, or the KLK5/ LL-37 inflammatory loop driving rosacea’s characteristic reactivity.

Skin renews itself continuously. New keratinocytes form at the stratum basale, mature through the viable epidermis over 40–60 days, and eventually reach the stratum corneum surface as structurally complete corneocytes ready to be shed. What controls the shedding is not a passive wear-and-tear process – it is a tightly regulated enzymatic timer that determines precisely where and when corneodesmosomal adhesion is dismantled. Get the timing right and the stratum corneum maintains constant thickness with intact barrier function throughout. Get it wrong in either direction and the consequences extend well beyond skin texture: barrier integrity fails, antimicrobial defences are dysregulated, and in some presentations the desquamation machinery becomes the entry point for a self-amplifying inflammatory cycle. ^[3]

The corneodesmosome: what gets cut

Corneocytes are held together in the stratum corneum by corneodesmosomes – specialised adhesion structures distinct from the desmosomes of the viable epidermis. Three proteins form their extracellular domain: desmoglein 1 (DSG1), desmocollin 1 (DSC1), and corneodesmosin (CDSN). All three must be cleaved for a corneocyte to release. The consequences of losing any single component are severe: corneodesmosin gene ablation in mice produces lethal skin barrier disruption, confirming it is not redundant with DSG1 and DSC1 but performs a distinct structural role. ^[7]

Corneodesmosomes are present throughout the stratum corneum but exist in a gradient of degradation: intact in the lower layers, progressively cleaved through the mid-layers, and absent at the surface where shedding occurs. That gradient of degradation is what maintains the stratum corneum as a cohesive structure whilst allowing continuous renewal at its outer face. The serine proteases that perform this cleavage – KLK5, KLK7, and KLK14 – are co-delivered into the SC extracellular space via lamellar body secretion alongside ceramide precursors. The desquamation enzymes and the barrier lipids arrive from the same organelle, which means lamellar body secretion defects impair both barrier construction and desquamation control simultaneously. ^[10]

The KLK/LEKTI pH timer

KLK5 is the primary driver. It cleaves DSG1, DSC1, and CDSN directly, and activates KLK7 and KLK14 through proteolytic cascades, amplifying desquamation activity. Pro-KLK5 undergoes auto-activation at the SG–SC interface under the acidic conditions there. Left unchecked, it would cleave corneodesmosomes throughout the entire SC depth – producing continuous shedding from the inside out rather than controlled surface release. ^[2]

LEKTI (lympho-epithelial Kazal-type inhibitor, encoded by SPINK5) is the brake. Produced in the stratum granulosum, LEKTI generates multiple inhibitory fragments that bind KLK5, KLK7, and KLK14 with high affinity – the D8–D11 domain fragment binds KLK5 in a reaction described as rapid and essentially irreversible under acidic conditions. In the acidic mid- and lower SC (pH 4.7–5.5), that binding is sustained. KLK5 is held inactive. Corneodesmosomes remain intact. ^[2]

The spatial release mechanism is pH-driven. As corneocytes migrate toward the near-neutral surface (upper SC pH approximately 6.7, per Fukuda et al. 2024), LEKTI dissociates from KLK5 at the higher pH. Active, uninhibited KLK5 cleaves DSG1, DSC1, and CDSN. The corneocyte releases. Shedding begins precisely at the surface because the acid mantle pH gradient controls exactly where the inhibitor lets go. Fukuda 2024 confirmed this computationally. Simulating uniform pH 7.0 throughout the SC produced active KLK5 at all depths, with premature desquamation beginning in the lower half of the SC rather than at the surface. The three-zone pH gradient is not incidental to controlled shedding – it is the structural requirement for it. ^[4]

Three patterns of disrupted desquamation

Incomplete desquamation – retention and roughness

When KLK5 activity is insufficient or blocked, corneodesmosomes persist beyond the surface. Corneocytes accumulate, the SC thickens, and skin takes on the rough, dull, congested texture that clients often describe as skin that never looks clean. A skin equivalent model with attenuated KLK activity produced measurable SC thickening and persistent corneodesmosin immunoreactivity throughout the SC – corneocyte retention rather than shedding. ^[8]

Hard water contributes two independent mechanisms to this pattern. First, calcium and magnesium deposits raise surface pH, maintaining a more alkaline SC environment – but rather than releasing LEKTI early, the effect is to shift the entire gradient toward neutral, partially blunting the surface pH rise that normally triggers LEKTI dissociation in the upper SC. Second, mineral deposits physically inhibit KLK5 and KLK7 enzymatic activity directly, impairing corneodesmosomal cleavage regardless of the pH state. Excess acid product use creates the same retention pattern through the opposite pH mechanism: too-acidic conditions throughout maintain LEKTI binding too broadly, suppressing KLK5 activation even at the surface.

Accelerated desquamation – premature shedding and barrier loss

When LEKTI fails to hold KLK5 inactive in the lower and mid-SC, corneodesmosomal cleavage begins prematurely. The stratum corneum sheds before it has completed its structural and barrier function. In Netherton syndrome, caused by homozygous SPINK5 loss-of-function mutations, this is absolute: KLK5 inactivation in SPINK5-null mouse models completely reverses the cutaneous hallmarks, confirming KLK5 overactivity as the operative mechanism rather than the SPINK5 loss itself. ^[5]

Alkaline pH conditions drive a functionally milder but clinically significant version of this pattern in everyday skin. When acid mantle disruption raises mid-SC pH above 6.0, LEKTI–KLK5 binding weakens at depths where it should remain intact, shifting the effective shedding initiation point deeper into the SC. Retinoids accelerate desquamation through an entirely distinct mechanism: downregulation of DSG1 and DSC1 expression rather than KLK upregulation. Retinoid-induced scaling is therefore independent of the pH/KLK axis, which is why acid mantle restoration alone does not fully resolve it. ^[6]

The rosacea loop – KLK5 overexpression and LL-37 excess

KLK5 cleaves cathelicidin precursor hCAP-18 to produce the antimicrobial peptide LL-37. In healthy skin, surface-limited KLK5 activity produces LL-37 in modest, appropriately localised amounts. In rosacea skin, KLK5 is overexpressed and its activity extends deeper into the SC, generating excess LL-37 and structurally abnormal cathelicidin peptide fragments not found in healthy skin. ^[9]

Those fragments drive leukocyte chemotaxis, angiogenesis via VEGF upregulation, and NLRP3 inflammasome activation – producing rosacea’s characteristic vascular reactivity, flushing, and chronic erythema. The vascular and inflammatory features of rosacea are downstream consequences of a KLK5 overactivity loop that begins at the SC level, not primarily vascular or immune dysregulation events. Excess LL-37 also directly activates mast cells and sensory nerve endings, connecting the KLK5 loop to the neurogenic inflammation and sensitivity characteristic of rosacea presentations. Elevated cathelicidin and KLK5 activity have been confirmed in biopsy samples from rosacea skin and post-treatment, with KLK5 activity normalising alongside clinical improvement. ^[1]

Restoring normal desquamation timing

Acid mantle restoration addresses both the incomplete and accelerated patterns driven by pH dysregulation:

• pH-appropriate cleansers (4.5–5.5) maintain LEKTI–KLK binding in the mid-SC where it should be sustained
• Hard water chelation, soft water washing, or post-wash chelating steps remove mineral deposits and restore the pH gradient the timer depends on
• NHE1 support and FFA generation maintain the acid mantle conditions that control LEKTI release at the surface

For rosacea presentations: polynucleotides suppress NF-κB-driven KLK5 overexpression alongside the innate immune environment driving excess LL-37 production. Azelaic acid directly reduces KLK5 activity in rosacea skin – one of its primary mechanisms rather than a general antimicrobial effect. CAP reduces the IL-4/ IL-13 and NF-κB-driven inflammatory amplification of KLK5 in reactive presentations.

For retinoid-induced desquamation: titrating retinoid use alongside barrier lipid support addresses the DSG1/DSC1 downregulation mechanism rather than attempting to counteract it with acid mantle optimisation alone. The two mechanisms are independent.

Clinical Pearl Clients who describe their skin as perpetually rough, dull, or never properly clean despite regular exfoliation often have incomplete desquamation from impaired KLK5 activity – not insufficient exfoliation. Mechanical exfoliation removes accumulated corneocytes symptomatically without addressing the enzymatic cause. In hard water areas, the more effective intervention is restoring the acid environment and removing mineral deposits that directly block KLK5 and KLK7 activity. Recommending a chelating toner, a pH-appropriate cleanser, and a water softener addresses the mechanism; recommending a stronger exfoliant does not, and risks impairing the barrier further.