Skin Structure

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Skin Physiology — The Blueprint for Formulation

In my formulation research, the efficacy of any batch is determined by its interaction with the skin’s biological structure. To formulate effectively, we must understand the “Target Zone.” While most topically applied cosmetics only interact with the Epidermis, their role in supporting the barrier function is critical.

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1. The Epidermis: The Barrier Architecture

The Epidermis is a dynamic system of transformation. Keratinocytes are born in the deepest layer and migrate upward, undergoing a process of keratinization until they reach the surface.

• Stratum Corneum (SC): The “Shield.” It consists of flattened, dead corneocytes that are constantly shedding.

• Stratum Lucidum: A specialized, translucent layer found only on the palms and soles (high-friction areas).

• Stratum Granulosum: The transition zone where cells begin to flatten and lose their nuclei.

• Stratum Spinosum: The “Spinous” layer where proteins and lipids are synthesized to provide structural integrity.

• Stratum Basale (Basal Layer): The site of cell birth. This layer also houses Melanocytes (pigment), Langerhans cells (immunity), and Merkel cells (touch).

2. The “Bricks and Mortar” Model

In the Stratum Corneum, cells follow a specific structural theory often referred to as the “Bricks and Mortar” model.

• • The Bricks (Corneocytes): These flat cells are held together by Corneodesmosomes—strong protein “strings.”

  • The Mortar (Lipid Matrix): A pool of ceramides, cholesterol, and fatty acids that makes the skin water-resistant.

  • Natural Moisturizing Factor (NMF): Inside the corneocytes sits a mixture of hygroscopic compounds (Urea, Lactic Acid, Amino Acids). In my lab notes, I prioritize ingredients that mimic the NMF to attract and bind water to the skin.

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3. The Dermis: The Support Matrix

The Dermis provides the structural “scaffolding” and nutrient supply for the skin.

• The Extracellular Matrix: A “cushion” containing Collagen (strength), Elastin (elasticity), and Glycosaminoglycans (like Hyaluronic Acid).

• Fibroblasts: The “builders” that produce these fibers.

• The Glandular System: Including sebaceous glands (sebum production) and sweat glands.

Researcher Observation: Most cosmetic formulations are designed to support the Epidermis. When we add Hyaluronic Acid or Ceramides, we are essentially reinforcing the “Mortar” or the “NMF” of the Stratum Corneum to prevent Transepidermal Water Loss (TEWL).