This site is an educational science resource published by SerucellBio Inc. It describes the biology of intercellular skin signaling. It does not constitute medical advice and makes no clinical efficacy claims for any product. For KFS® product information, visit serucell.com.
Intelligent Skin Signaling
Skin health is a conversation.
Between your epidermis and dermis. Between keratinocytes and fibroblasts. A continuous exchange of signals that coordinates everything your skin does — and one that changes, silently, decades before it shows on the surface.
Scroll to explore the biology ↓
01 — The Signal System
Your skin is two systems that must speak to survive.
The epidermis — your outermost skin — is built primarily of keratinocytes. The dermis beneath it is the structural layer, populated by fibroblasts. These two populations do not function independently. They are in constant biochemical dialogue.
Keratinocytes signal downward through the dermal-epidermal junction (DEJ), triggering fibroblast behavior. Fibroblasts signal upward through the same interface, influencing how keratinocytes differentiate, proliferate, and maintain the skin barrier. This bidirectional paracrine communication is not incidental to skin health — it is skin health.
- Keratinocytes — Epidermal layer: Barrier maintenance · Barrier renewal.
- Fibroblasts — Dermal layer: Collagen synthesis · Matrix architecture.
The Dermal-Epidermal Junction (DEJ). The interface where this communication is mediated — a basement membrane structure that physically separates yet biochemically connects the two cell populations. Its integrity is central to how well the signal travels in both directions. The signals that emerge from their interaction are different — and more complete — than anything either produces in isolation.
02 — When Signals Fail
Aging is not about losing collagen. It is about losing the signal that makes collagen possible.
The central mechanism of skin aging is not cosmetic. It is cellular. Over time, dermal fibroblasts undergo a process called senescence.
- 35% Reduction in fibroblast density in aged skin — fewer cells to maintain and renew the dermal matrix. Frontiers in Pharmacology, 2025
- 68% Reduction in type I procollagen synthesis — the primary structural protein behind skin firmness. Frontiers in Pharmacology, 2025
- 30% Decrease in collagen-synthetic capacity in aged fibroblasts — even in cells that remain active. Frontiers in Pharmacology, 2025
- 1 · Trigger — Permanent cell cycle arrest: Fibroblasts subjected to DNA damage, oxidative stress, telomere attrition, or mitochondrial dysfunction stop dividing. They cannot be replaced by their own replication.
- 2 · Consequence — The SASP: Senescent fibroblasts shift into a pro-inflammatory secretory state, releasing cytokines (IL-6, IL-8, IL-1β, TNF-α, MMP enzymes) that degrade the matrix and disrupt the paracrine signals keratinocytes depend on.
- 3 · Effect — Communication breakdown: The signal keratinocytes receive from the dermis changes from regenerative to inflammatory. The conversation that coordinates skin renewal becomes noise.
03 — The Secretome
The signal is not a single molecule. It is a system.
A secretome is the complete set of proteins a cell secretes into its environment under a given condition. When keratinocytes and fibroblasts are co-cultured under the right conditions, the secretome they produce together is fundamentally different from the secretome either cell produces alone. The paracrine interaction produces proteins that do not exist in either monoculture. This is measurable.
- «HOLD» Total proteins in the KFS® co-culture secretome by mass spectrometry. [HOLD — protein count pending verification: 969 vs 962; update all four sites together]
- 385 Proteins present exclusively in co-culture — absent from keratinocyte-only and fibroblast-only secretomes.
- 40% The fraction of the KFS® secretome that exists only because both cell types were present and signaling to each other.
You cannot replicate these proteins by combining monoculture secretomes. The live paracrine dialogue is what produces them. This is why co-culture is not a method of production — it is a biological requirement.
KFS® — Keratinocyte Fibroblast Serum is this secretome, collected and formulated for topical use. What it looks like on skin — independently assessed, dermatologist-conducted, 12 weeks: 43% improvement in overall skin appearance, 90% in smoothness, 76% in radiance, zero adverse events. The biology explains why it was worth studying. The study shows what it looks like. → View the Draelos study at serucell.com
04 — Where It Comes From
The signal comes from the right cells at the right moment.
The biological output of a cell is not fixed. It is determined by the cell’s age, condition, signaling environment, and the state of the cells around it. A senescent fibroblast and a healthy young fibroblast do not produce the same secretome. The age and health of the source cell determines the character of the signal it produces.
- Source qualification: KFS® is produced from human keratinocytes and fibroblasts sourced under stringent donor and lot criteria — cell source age, passage number, lot consistency controlled for biological character, not just sterility.
- Manufacturing: Production is conducted under controlled conditions by SerucellBio Inc. via the patented stress-induction co-culture process (five U.S. patents), designed to maintain the paracrine dialogue during collection — because interrupting it changes what is collected.
05 — Collection Science
The way you collect a signal determines whether you collect it at all.
Standard conditioned-media collection harvests what cells secrete at rest. The KFS® manufacturing process is different in mechanism, not degree.
The Stress-Induction Protocol. After the co-culture is established and the paracrine dialogue is active, the growth medium is replaced with a collection medium that deliberately withholds specific growth factors. This controlled withdrawal induces a physiological stress response — shifting the secretome from a maintenance profile to a response profile. The proteins collected under stress are different from those collected at baseline. This protocol is patented — protected by five U.S. patents held by SerucellBio Inc.
What that collection process produces — and what it looks like on skin — is documented in a 12-week independent dermatologist study. → View the clinical study results
06 — Signal Across Time
The secretome is not a single moment. It is a conversation across time.
A cell under physiological stress responds with a sequence — an evolving output that changes character as the stress continues. SerucellBio’s research has characterized three distinct temporal phases of the stress-induced secretome.
- Stage 1 — Acute Alarm Response: The initial output following stress induction — early cytokines and rapid-response proteins, the cell’s first recognition of a changed environment.
- Stage 2 — Adaptive Stress Response · Lead Stage: The sustained phase. The cell has adapted and produces a characteristic set of proteins associated with cellular organization and response. This is the primary collection stage for KFS® — the most biologically complete output.
- Stage 3 — Terminal Stress Response: The late phase as cells approach end-of-viability under continued stress. Terminal-phase proteins, distinct from Stage 2 in character and composition.
Stage 2 is the lead stage because it represents the secretome at the point of maximum adaptive dialogue. Each stage is compositionally distinct; stage-selective collection produces a defined, consistent biological output.
07 — Signal-First
Not all conditioned media are the same. Now there’s a standard that says why.
The skincare market has no existing standard for conditioned-media cosmetic ingredients. The Intelligent Skin Signaling™ Standard was developed because the biology demands specificity: if the mechanism is paracrine co-culture signaling, the ingredient must demonstrate it was produced by paracrine co-culture signaling.
- 1 · Multi-Cell Co-Culture Origin: Produced by the simultaneous co-culture of two or more relevant cell populations — not monoculture or post-hoc blending.
- 2 · Stress-Induced Secretion Protocol: A defined physiological stress-induction step that shifts the secretome from maintenance to response. Baseline conditioned media does not qualify.
- 3 · INCI Registration: Registered under its own INCI designation, reflecting its co-culture origin and distinct compositional profile.
- 4 · Independent Clinical Characterization: Effects on skin appearance characterized in an independent, controlled clinical study — not a self-reported panel or internal test.
KFS® — Human Keratinocyte Fibroblast Saline Conditioned Media — meets all four ISS Standard criteria: produced by stress-induction co-culture (1 & 2), registered under its own INCI designation (3), and characterized in an independent 12-week dermatologist-conducted study showing 43% improvement in overall skin appearance, investigator-assessed (4; Study DCS-24-19). → Visit serucell.com to see what meeting this standard looks like on skin.
08 — Research
The biology, measured.
The Draelos Study (DCS-24-19). Conducted by Zoe Diana Draelos, M.D., Dermatology Consulting Services, High Point, NC — one of the most published cosmetic dermatologists in the U.S. No ongoing financial relationship with Serucell; conducted independently at her research facility. 12-week monadic study, 25 enrolled / 24 completers, healthy females ages 30–50, Fitzpatrick I–VI, KFS® Facial Serum twice daily, Wilcoxon signed-rank analysis (p≤0.05).
| Metric (investigator-assessed, 12 wks) | Improvement | P-Value |
|---|---|---|
| Overall Skin Appearance | 43% | p<0.001 |
| Dryness | 92% | p<0.001 |
| Tactile & Visual Smoothness | 90% | p<0.001 |
| Radiance | 76% | p<0.001 |
| Luminosity | 75% | p<0.001 |
| Skin Texture | 56% | p<0.001 |
| Firmness | 28% | p<0.05 |
| Adverse Events | Zero | — |
- 11% Corneometry — improvement in skin hydration at Week 12 (p=0.024).
- 17% Elasticity — improvement at Week 6 (p<0.001).
- Sig. Dermaspectrophotometry — reduction in dyspigmentation at Week 12 (p<0.001).
[HOLD — investigator quote: do not publish until verbatim wording is approved in writing by Dr. Draelos.]
Exploratory histology. Instrument-quantified digital histomorphometry (iHisto; Indica Labs Halo). Dataset 1 (single subject, 6 weeks): +69% collagen-associated staining, +82% elastin fiber signal, +12% collagen staining intensity. [HOLD — Dataset 2 omitted pending iHisto DS2 anomaly resolution.] These are instrument-quantified observations in a single subject. They do not constitute proof of collagen or elastin synthesis. Single subject. Exploratory. Multi-subject validation in planning.
The biology described on this site predicts that a characterized co-culture secretome would show up differently on skin than isolated actives. The study shows what that looks like: 43% improvement in overall skin appearance, investigator-assessed, 12 weeks, zero adverse events. That is the ISS Standard, demonstrated.
- → Shop KFS® at serucell.com
- → View the full clinical study at serucell.com
- → Explore the platform science at intelligentcellsignaling.com
A SerucellBio Inc. Platform Science Resource. intelligentskinsignaling.com describes the biology of skin cell signaling and the science basis for the Intelligent Skin Signaling™ Standard. It is an educational resource. Clinical product information: serucell.com · Platform science: intelligentcellsignaling.com · IP & entity: serucell.bio. © 2026 SerucellBio Inc. All rights reserved. KFS® is a registered trademark. Intelligent Skin Signaling™ and Multi-Cell Technology™ are trademarks of SerucellBio Inc.