Common misconceptions about the stratum corneum
The stratum corneum is the outermost layer of the epidermis, often misunderstood as a dead, impermeable barrier. This article addresses common misconceptions and reviews research on penetration enhancement and barrier fu
What is the stratum corneum?
The stratum corneum (SC) is the outermost layer of the epidermis, also known as the horny layer. It is a class of biological barrier composed primarily of corneocytes (dead, flattened keratinocytes) embedded in a lipid matrix. The SC is not a single entity but a complex structure with a thickness typically around 10–20 µm, though this varies by body site. Its primary function is to limit water loss and protect against environmental insults. The SC is often described as a brick-and-mortar model, where corneocytes are the bricks and intercellular lipids (ceramides, cholesterol, fatty acids) are the mortar.
Research on SC penetration and barrier function centres on the intercellular lipid pathway and the role of tight junctions in the stratum granulosum, as well as the physicochemical properties of permeants.
Research Studies
Biodegradable STAR particles and skin permeability
STAR particles (microscopic needles) have been developed to painlessly puncture the skin and increase permeability. Traditionally made of non-biodegradable materials like ceramic and metal, recent work introduced biodegradable polymer STAR particles that are water-soluble (poly(vinyl alcohol), PVA), enzyme-degradable (cellulose acetate, CA), or hydrolyzable (polylactic acid, PLA). These particles were designed to address environmental and safety concerns while enhancing drug delivery to skin [1].
Hybrid lipid-polymeric nanoparticles for co-delivery of CoQ10 and siRNA TNFα
In inflammatory skin diseases such as psoriasis, topical therapies are limited by poor skin penetration and single-target mechanisms. Hybrid lipid-polymeric nanoparticles (HLPNs) were developed for co-delivery of coenzyme Q10 (CoQ10), an endogenous antioxidant, and siRNA TNFα. This approach aims to simultaneously modulate inflammatory and oxidative pathways [2].
Topical formulation with panthenol, niacinamide, and dipotassium glycyrrhizate in xerosis
A 28-day randomized, split-leg, untreated-controlled trial evaluated a topical formulation containing panthenol, niacinamide, and dipotassium glycyrrhizate in individuals with xerosis cutis. The study assessed skin hydration and barrier function, measuring transepidermal water loss (TEWL) and hydration. The formulation was applied twice daily to one pretibial area, with the contralateral leg as control [3].
Emulgel with hyaluronic acid and sh-oligopeptide-1 in paediatric atopic dermatitis
An emulgel containing hyaluronic acid, glycerol, grape seed oil, Calendula officinalis, aloe vera, and sh-oligopeptide-1 (a synthetic epidermal growth factor) was tested in a randomized, self-controlled trial in 57 children (aged 2–14) with atopic dermatitis. The emulgel was applied twice daily for 10 days to one forearm, with the other forearm as control. Skin barrier parameters including TEWL, stratum corneum hydration (SCH), erythema, and pH were measured [4].
Acetyl hexapeptide-8 and skin permeability
Acetyl hexapeptide-8 (AH-8), often referred to as a "botox-like" peptide, is a biomimetic peptide used in cosmeceuticals for its potential to reduce wrinkles by modulating neuromuscular activity. A review focused on its skin permeability and efficacy, discussing its structure, proposed mechanisms, and use in topical formulations for anti-aging, scar treatment, and skin rejuvenation [5].
Palmitoyl hexapeptide-12 and mechanical interaction with skin components
Palmitoyl hexapeptide-12, a self-assembling peptide, was studied for its short-term impact on skin composition and mechanics. Using label-free techniques including orbital trapping secondary ion mass spectrometry (OrbiSIMS), researchers tracked its self-assembly and penetration within full-thickness human skin, distinguishing between sol and gel forms [6].
Oral NatureU® Mind Care BeautyU Caps and skin aging parameters
A 56-day, single-center, open-label, single-arm exploratory study evaluated changes in skin-aging parameters after daily oral intake of NatureU® Mind Care BeautyU Caps in adult women. The primary outcome was change in crow's-feet wrinkle count at Day 56 assessed by PRIMOS CR imaging. Secondary outcomes included stratum corneum hydration measured by Corneometer CM 825, as well as other wrinkle topography, elasticity, radiance, pigmentation, pore-related parameters, and dermal thickness [7].
Glycyrrhizic acid ionic liquid nanomicelles for transdermal delivery of signal peptides
Bioactive ionic liquids synthesized from natural glycyrrhizic acid (GA) and oxymatrine (OMT) were prepared to enhance transdermal delivery of anti-photoaging signal peptides. The GA-OMT (GAO) system improved the solubility of palmitoyl pentapeptide-4 (PAL-4), a model peptide drug, and facilitated its penetration. Molecular dynamics simulations and density functional theory calculations were used to optimize component ratios and formation mechanisms [8].
Comparison of penetration enhancement approaches
| Approach | Mechanism | Model | Reference |
|---|---|---|---|
| STAR particles (PVA, CA, PLA) | Microscopic needles puncture skin | In vitro / ex vivo (not specified) | [1] |
| Hybrid lipid-polymeric nanoparticles | Co-delivery of CoQ10 and siRNA TNFα | In vitro / in vivo (not specified) | [2] |
| Topical formulation (panthenol, niacinamide, dipotassium glycyrrhizate) | Improves hydration and barrier function | Human clinical trial (xerosis) | [3] |
| Emulgel (HA, glycerol, etc.) | Improves barrier parameters | Human clinical trial (paediatric AD) | [4] |
| Acetyl hexapeptide-8 | Modulates neuromuscular activity | Review (human skin permeability) | [5] |
| Palmitoyl hexapeptide-12 | Self-assembly, mechanical interaction | Full-thickness human skin | [6] |
| Oral NatureU® Mind Care BeautyU Caps | Oral intake, systemic effects | Human clinical trial (adult women) | [7] |
| GA-OMT ionic liquid nanomicelles | Enhances solubility and penetration | In vitro / ex vivo (not specified) | [8] |
If you are reading this for personal health reasons
The materials and compounds discussed here are sold for laboratory research purposes only. We do not provide dosing, medical guidance, or recommendations for personal use. If you are considering any compound for yourself, you should speak to a licensed clinician.
Sources
- [1] Water-Soluble, Enzyme-Degradable, and Hydrolyzable STAR Particles for Enhanced Drug Delivery to Skin
- [2] A dual functional hybrid lipid-polymeric nanoparticle co-loaded coenzyme Q10 and siRNA TNFα for anti-inflammatory skin therapy
- [3] Efficacy of a Topical Formulation on Skin Hydration and Barrier Function in Individuals With Xerosis: A 28-Day Randomized, Split-Leg, Untreated-Controlled Trial
- [4] Update on the Research of an Emulgel for the Effective Treatment of Atopic Dermatitis: Clinical Investigation in Children
- [5] Acetyl Hexapeptide-8 in Cosmeceuticals-A Review of Skin Permeability and Efficacy
- [6] Noninvasive Monitoring of Palmitoyl Hexapeptide-12 in Human Skin Layers: Mechanical Interaction with Skin Components and Its Potential Skincare Benefits
- [7] A 56-Day Exploratory Study of NatureU® Mind Care BeautyU Caps on Skin Aging Parameters
- [8] Bioactive Glycyrrhizic Acid Ionic Liquid Self-Assembled Nanomicelles for Enhanced Transdermal Delivery of Anti-Photoaging Signal Peptides