Does PDRN cream absorb into the skin?

Sinking in is not the same as absorption

A minute or two after you apply a cream, the shine fades and the slippery feel under your fingertips disappears. People often call this fast absorption, but what is mostly happening is that the water in the formula evaporates and the remaining ingredients spread into a thin film on the skin. The feeling that a product has sunk in is one thing; “penetration,” where an ingredient passes through the stratum corneum and moves farther down, is another.

This distinction is also the starting point for judging the claim “low molecular weight, so it absorbs deeply.” What gets in, and how much, depends on the structure of the skin and the size of the molecule.

The stratum corneum is built like a brick wall

The stratum corneum, the skin’s outermost layer, is about 10–20 µm thick: one-tenth to one-fifth the thickness of a sheet of copy paper (about 0.1 mm). It is thin but tightly built. Flattened, hardened skin cells called corneocytes are stacked in many layers, and the gaps between them are filled with lipids made up of ceramides, cholesterol and fatty acids. The cells are often likened to bricks and the lipids to the mortar between them, and it is mainly these lipids that act as the barrier keeping water from escaping.¹

Substances from outside have three main routes through this layer: a winding path through the lipids between the corneocytes, a direct path straight through the cells and a path down the hair follicles. Most ingredients take the first route.¹ That path is only nanometers wide and oily in character, so small molecules that dissolve reasonably well in both water and oil get through easily, while large or strongly charged molecules do not.

The 500 Dalton rule of thumb

In 2000, Dutch dermatology researchers Bos and Meinardi drew attention to a common thread: substances that cause allergic reactions on contact with the skin, drugs applied to the skin and drugs delivered through skin patches almost without exception have a molecular weight below 500 daltons. They named this the “500 Dalton rule.”²

Despite the name, it is really a rule of thumb drawn from observation. Around 500 daltons, the outcome depends on the properties of the ingredient and the formula, and it also varies with the condition of the skin. Still, the overall pattern, that intact skin becomes sharply harder to cross as molecules get bigger, is widely accepted in dermatology. Pharmaceutical science likewise holds that delivering large molecules through the skin takes special techniques to get past the stratum corneum barrier.³

Picturing 97 kDa

PDRN is a mix of DNA fragments of varying lengths, so no single molecular weight can be quoted for it; it is described by an average instead. The certificate of analysis for PYDERIN’s raw material lists an average size of 150 bp (base pairs). In double-stranded DNA, each base pair weighs about 650–660 daltons, so 150 bp comes to about 97–99 kDa. The 97 kDa figure PYDERIN gives for its products is 97.5 kDa, calculated at 650 daltons per base pair and rounded down.⁴

Pictured as a shape, it is a thin rod about 2 nm across and about 50 nm long, since the DNA double helix grows 0.34 nm longer with each base pair. DNA of this length behaves much like a stiff rod, and the phosphate groups in its backbone give it a strong negative charge and make it very water-loving. That is almost exactly the opposite of the profile we saw earlier for molecules that pass easily through the stratum corneum.

So is “low-molecular-weight PDRN” an accurate description? It depends on the yardstick. The research literature usually describes PDRN as a mixture of DNA fragments with molecular weights of 50–1,500 kDa, and one classification puts fragments under 50 kDa in a separate low-molecular-weight PDRN group.⁵ By that classification, an average of 97 kDa sits at the small end of the usual PDRN range. By any yardstick, though, it is a very large molecule next to 500 daltons, the threshold for the skin barrier. When you see “low molecular weight,” first check what it is being compared with.

Where applied PDRN stays

Taken together, the evidence indicates that most of the PDRN you apply remains on the skin’s surface and in the upper layers of the stratum corneum. DNA is a large, water-loving molecule, so it has a hard time working its way into the narrow, oily paths through the lipids.

What about hair follicle openings?

Studies have found that dyes and fine particles applied to the skin collect in hair follicle openings and stay there for a while,⁶ and the forehead, where follicles are most densely packed, has relatively more of this space.⁷ However, we found no study in human skin confirming that PDRN stays in follicle openings in this way.

What matters when you apply it

Molecular size is the starting point, but other variables also change the outcome. The amount that passes through the skin is proportional to the difference in concentration between the outside and the inside of the skin, and the same ingredient behaves differently depending on the formula it is in and how hydrated the skin is.⁸ The tips below help what you apply spread evenly and stay on the skin longer. They are not ways to push PDRN into the skin.

Products spread more evenly when your skin is still damp, such as right after cleansing or after toner. Finishing with a cream reduces water loss and helps your skin stay hydrated for longer. Studies have found that covering the skin (occlusion) often increases how much of an ingredient penetrates,⁹ but most of those results involve small molecules, so they can’t simply be extended to a large molecule like PDRN.

Don’t exfoliate on the same day you try a new product for the first time: right after exfoliating, a new product is more likely to sting. Avoid using cosmetics on broken skin, and if you are seeing a doctor for a skin condition, check with your doctor before using cosmetics.

Why PYDERIN discloses size and purity

PYDERIN discloses its 97 kDa and 99% purity figures because they can be checked against the certificate of analysis. PDRN raw materials can differ in size distribution and level of purification from one supplier to another, so a stated average size and purity give you a basis for comparing which raw material was used. The certificate for PYDERIN’s raw material records an average size of 150 bp, 99% DNA purity, an A260/A280 ratio of 1.78 (a gauge of whether protein is mixed in) and no detectable levels of four heavy metals. The 97 kDa figure in PYDERIN’s product information is a representative value, converted to weight from this lot’s measurement; the raw material’s specification calls for an average of 30–200 kDa. We explain what each of these unfamiliar numbers measures in How to read the numbers on a PDRN label.

How a cream feels and how well it moisturizes depend largely on the ingredients that come with the PDRN. REJUVUSTER PDRN Rejuvenating Cream, for example, lists moisturizing ingredients such as panthenol, ceramide NP and squalane alongside its PDRN. We look at what each ingredient contributes in Ingredients to use with PDRN.

• REJUVUSTER · Partner pharmacies (Korea) REJUVUSTER PDRN Rejuvenating Cream A cream combining 97 kDa PDRN with panthenol, ceramide NP and squalane View product
• PYDERIN · Partner clinics (Korea) PDRN Lift Cream A cream that adds panthenol, 7 types of collagen and acetyl hexapeptide-8 to PDRN. The ingredient list includes fragrance View product
• HYDROVUSTER · Partner pharmacies (Korea) PYDERIN HYDROVUSTER PDRN Re-Barrier Soothing Cream A cream with 3% panthenol, ceramide NP and squalane alongside PDRN View product

This article is general information to help you choose and use cosmetics. It is not a substitute for the diagnosis or treatment of any condition. If you have a skin problem, consult a dermatologist.