Polynucleotides
4 min readInjectable PDRN vs Topical 'Salmon DNA' Serums
Educational reading for licensed practitioners — not clinical or injection guidance.
Search interest in "salmon DNA" skincare has exploded alongside the rise of polynucleotide injectables, and the two are often spoken about as if they were the same treatment in different packaging. They are not. An injectable delivers purified DNA fragments into the living dermis; a serum sits on the surface. Understanding why that difference matters is the difference between a realistic purchase and a disappointed one.
What PDRN and Polynucleotides Actually Are
Polynucleotides (PN) are long chains of nucleotides — the building blocks of DNA — most often purified from the sperm DNA of salmon or trout, species whose DNA fragments are highly biocompatible with human tissue. PDRN (polydeoxyribonucleotide) is a specific, well-characterised fraction of these fragments. Both are large, water-loving, negatively charged molecules. That chemistry is central to what follows: it is exactly what makes them useful once they are placed in the skin, and exactly what stops them getting there through a cream.
Injectable ranges such as Plinest and Newest are formulated as sterile gels for placement in the dermis. A topical serum labelled "salmon DNA" or "PDRN" is a cosmetic designed to sit on and within the outermost layers.
The Stratum Corneum Problem
The skin's outermost layer, the stratum corneum, is a deliberate barrier: a compact, lipid-rich wall whose entire biological job is to keep large foreign molecules out and water in. Dermatology has a useful rule of thumb — often called the 500 Dalton rule — that molecules much heavier than roughly 500 daltons struggle to cross intact skin in any meaningful quantity by passive diffusion.
Polynucleotide and PDRN molecules are enormous by that measure, running into the tens or hundreds of kilodaltons, and they are hydrophilic and charged as well as large. In other words they fail the penetration test on every count. A serum can deposit them on the surface, but the intact barrier keeps the vast majority from travelling down to where the target cells live.
Where the Injectable Works: The Dermis
Fibroblasts — the cells that produce collagen and elastin — sit in the dermis, well below the barrier. A needle bypasses the stratum corneum entirely and places polynucleotides directly in that environment, where they are understood to support fibroblast activity, encourage the formation of small blood vessels, exert antioxidant and anti-inflammatory effects, and act as a hydrating scaffold. That is the whole point of injecting rather than applying: it puts the active exactly where the biology happens.
It is worth stating plainly for compliance and honesty: no injectable polynucleotide or PDRN product is FDA-approved. These are CE-marked devices used internationally, and results build gradually over a course rather than appearing overnight.
What a Topical PDRN Serum Can and Can't Do
None of this makes a good serum worthless — it just changes the claim. A well-formulated topical containing polynucleotides, such as the Mastelli polynucleotide turnover cream or a leave-on like Nithya Mousse, can support the surface: improving the feel of the skin, contributing to hydration and comfort, and playing a useful role in post-procedure aftercare. What it cannot credibly claim is to reproduce the fibroblast-level regeneration of an injection, because the molecule that would drive that never reaches the fibroblast in appreciable amounts.
Framed correctly, the two are complementary rather than competitive: the injectable does the deep regenerative work; the serum supports the barrier and comfort of the skin around it.
Bridging the Gap: Delivery Matters
The one honest way to move a large active past the barrier without a syringe is to breach the barrier mechanically. Controlled microneedling creates transient channels that can improve delivery of applied actives, which is why microneedling-plus-polynucleotide protocols exist and why serums are often paired with a needling step rather than relied on alone. Even then, delivery is a partial workaround, not equivalence — the depth, dose and distribution of an injection remain difficult to match topically.
The Takeaway
The barrier is doing its job, and that is precisely why topical "salmon DNA" serums cannot stand in for the injectable. Injected polynucleotides reach dermal fibroblasts; serums largely do not, and should be judged as barrier-supporting skincare rather than a needle-free version of the treatment. If the goal is genuine dermal regeneration, the delivery route is not a marketing detail — it is the treatment.
For clinic use, explore the polynucleotide injection range on the catalogue.