Patch Absorption Science

Lily M.
April 29,2025

Title

A deep dive into transdermal bioavailability the research behind how ingredients cross your skin, what determines absorption rates, and why delivery method matters as much as the ingredients themselves.

Why Absorption Matters More Than Dosage

A 1000mg supplement means nothing if only a fraction reaches your bloodstream. Bioavailability — the percentage of an active ingredient that actually enters systemic circulation — is the real measure of a supplement's effectiveness.

When a drug or supplement is administered intravenously, its bioavailability is 100% by definition. Every other delivery route — oral, sublingual, transdermal — delivers less than 100%, but the losses vary dramatically depending on the path the ingredient takes.

For oral supplements, the journey through stomach acid, intestinal absorption, and hepatic first-pass metabolism can reduce bioavailability significantly. Transdermal delivery bypasses these barriers, offering a more direct route to the bloodstream.

The Two Penetration Pathways

When ingredients leave the patch and enter the skin, they can take one of two routes through the stratum corneum:

Diagram showing intercellular and transcellular pathways through skin cells. Size: 1200 x 550px

Intercellular Pathway (Between Cells)

The dominant route for most transdermal ingredients. Molecules navigate through the lipid matrix that fills the spaces between dead skin cells (corneocytes). This winding path favors lipophilic (fat-soluble) compounds that can dissolve into the skin's lipid layers. Most wellness patch ingredients use this pathway.

Transcellular Pathway (Through Cells)

A more direct but less common route where molecules pass directly through the corneocytes themselves. This pathway requires alternating between lipid and aqueous environments, making it more suited to very small, hydrophilic molecules.

Both pathways ultimately deliver ingredients through the viable epidermis and into the dermis, where capillary blood vessels absorb them into systemic circulation.

What Determines How Much Gets Absorbed?

Transdermal absorption follows Fick's First Law of Diffusion — the foundational principle of all transdermal science. In simple terms, absorption rate depends on five key factors:

01

Molecular Size

Smaller molecules penetrate skin more easily. The general threshold is 500 Daltons — molecules below this weight cross the stratum corneum efficiently. Most wellness ingredients used in Duori patches fall within this range, which is precisely why they were selected for transdermal delivery.

02

Lipophilicity (Fat Solubility)
The stratum corneum is rich in lipids, so fat-soluble compounds pass through more easily than water-soluble ones. However, the ingredient also needs some water solubility to partition into the aqueous viable epidermis below. The ideal balance is measured by log P (partition coefficient) — too lipophilic and it gets stuck in the outer skin layer; too hydrophilic and it can't enter.

03

Concentration Gradient
Ingredients naturally diffuse from high concentration (in the patch) to low concentration (in the skin and bloodstream). A well-designed patch maintains this gradient throughout its wear time, ensuring consistent delivery from first hour to last.

04

Surface Area & Duration
Larger patch contact area and longer wear time both increase total delivery. This is why Duori patches are designed with optimized dimensions for their specific ingredient loads, and recommended wear times are calibrated to maximize absorption.

05

Permeation Enhancers
These are safe, well-studied compounds included in patch formulations that temporarily increase the skin's permeability. They work by disrupting the organized lipid structure of the stratum corneum, creating temporary pathways for ingredient molecules to pass through more efficiently.

Oral vs. Transdermal: What the Research Shows

Clinical research across multiple compounds demonstrates the pharmacokinetic advantages of transdermal delivery over oral administration:

Transdermal delivery has been shown to provide a more favorable pharmacokinetic profile with lower peak concentrations (reducing side effects), longer time at steady-state levels (improving efficacy), and extended half-life compared to oral forms of the same compounds.

Frequently Asked Questions

Does transdermal delivery work for all ingredients?

No. Only molecules that are small (under 500 Daltons), lipophilic, and potent at low doses are suitable for transdermal delivery. This is why Duori specifically selects ingredients with molecular profiles compatible with skin absorption. Ingredients that don't meet these criteria are better delivered orally or by other routes.

How does Fick's Law apply to wellness patches?

Fick's Law describes how molecules move from areas of high concentration to low concentration across a barrier. In transdermal patches, the high concentration is in the patch matrix, and the low concentration is in your skin and bloodstream. The rate of transfer depends on the ingredient's properties, the skin's thickness, and the patch's design.

What are permeation enhancers and are they safe?

Permeation enhancers are compounds that temporarily and reversibly increase skin permeability to improve ingredient absorption. Common enhancers include fatty acids, alcohols, and terpenes. They've been extensively studied and are considered safe for topical use — they're found in many FDA-approved transdermal prescription products.

Can I increase absorption by applying the patch to thinner skin?

Yes — within reason. Areas with thinner skin and better blood flow (inner wrist, upper arm, shoulder) generally absorb more efficiently than areas with thicker skin. However, always follow the specific product's application guidelines and avoid damaged or irritated skin.

See the Science in Action

Now that you understand the science, explore our patches designed to maximize transdermal absorption.

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