Abstract
Background. Polynucleotides (PN/PDRN), platelet-rich plasma (PRP) and exosome preparations are increasingly offered as "regenerative" alternatives or adjuncts to hyaluronic acid biostimulation. They are routinely conflated in marketing but differ profoundly in molecular mechanism, evidence quality, manufacturing reproducibility and regulatory status.
Objective. To compare randomised controlled trial (RCT) evidence, histological correlates and UK/EU regulatory positioning of the three modalities between 2022 and 2026, and to derive a defensible clinical framework for practice.
Methods. Pragmatic review of MEDLINE-indexed RCTs, systematic reviews and meta-analyses (2022–2026); appraisal of MHRA, EMA and FDA regulatory communications; and review of UK ATMP guidance.
Findings. PN/PDRN now has multiple positive RCTs in periorbital photoageing, acne scarring and androgenetic alopecia, with consistent histological remodelling signals. PRP retains the largest evidence base but heterogeneity in preparation (DEPA, MARSPILL, PAW classifications) limits cross-trial comparability. Exosomes show pooled wrinkle improvement in meta-analyses but no authorised injectable product exists in the UK or EU, and the FDA has explicitly warned that no exosome product is approved for any cosmetic indication. A risk-weighted hierarchy is proposed.
1. Introduction
Between 2022 and 2026 the UK and EU aesthetic injectable market saw rapid uptake of three so-called "regenerative" modalities: polynucleotides (PN), most often as polydeoxyribonucleotide (PDRN) or salmon/trout-derived high-purity technology (PN-HPT); platelet-rich plasma (PRP); and exosome preparations marketed for topical or — in some unlicensed settings — injectable use. Practitioners frequently treat these three categories as interchangeable "skin boosters," yet they differ at every analytical level: molecular target, manufacturing pathway, evidence base, and legal authorisation.
This article restricts the evidence horizon to RCTs, systematic reviews and meta-analyses published between January 2022 and the time of writing in mid-2026, with selected earlier landmark trials retained when no successor has displaced them. Regulatory commentary draws on the Medicines and Healthcare products Regulatory Agency (MHRA), the European Medicines Agency (EMA), the European Commission's Advanced Therapy Medicinal Product (ATMP) framework, and the US FDA — the latter referenced because UK practitioners encounter US-sourced exosome supply.
Search Strategy
PubMed and Cochrane CENTRAL searched January 2022 – May 2026 using combinations of "polydeoxyribonucleotide", "polynucleotide", "platelet-rich plasma", "exosome", "extracellular vesicle", "skin rejuvenation", "alopecia", "photoageing" and "randomised". Regulatory sources: MHRA guidance on borderline products and ATMPs; EMA reflection papers on EV-based medicines; FDA Warning Letters database; UK Human Tissue Authority guidance.
2. Mechanisms of Action
2.1 Polynucleotides (PN/PDRN)
Polynucleotides are linear fragments of deoxyribonucleotides (typically 50–2000 kDa for PDRN; up to ~20 MDa for PN-HPT) derived from controlled enzymatic digestion of salmon or trout germ-cell DNA. Two complementary mechanisms are described. First, oligonucleotide fragments act as agonists at the A2A adenosine receptor on fibroblasts, downregulating tumour necrosis factor-alpha and upregulating vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-β) signalling — driving angiogenesis and matrix synthesis. Second, the salvage purine pathway recycles nucleotide fragments, supplying substrate for accelerated repair in metabolically active fibroblasts. Higher-molecular-weight PN preparations additionally form a viscoelastic scaffold that provides short-term hydromechanical support.
2.2 Platelet-Rich Plasma (PRP)
PRP is an autologous concentrate produced by single- or double-spin centrifugation of whole blood. The active fraction is α-granule release of platelet-derived growth factor (PDGF-AA/BB/AB), TGF-β1/β2, VEGF, epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF). Leucocyte content (L-PRP vs P-PRP) modulates the inflammatory profile, and platelet activation (calcium chloride, thrombin, mechanical disruption) determines kinetics of growth-factor release. The DEPA, MARSPILL and PAW classifications attempt to standardise reporting but remain inconsistently applied.
2.3 Exosomes / Small Extracellular Vesicles (sEVs)
Exosomes are 30–150 nm endosome-derived extracellular vesicles carrying micro-RNAs, messenger RNAs, lipids and surface proteins (CD9, CD63, CD81). Mesenchymal-stem-cell-derived (MSC-EV) and platelet-derived (PL-EV) preparations dominate the aesthetic market. The plausible cosmetic mechanism is paracrine cargo transfer — micro-RNAs (miR-21, miR-29, miR-146) modulating fibroblast collagen-I/III transcription, MMP-1 suppression and dermal angiogenesis. Unlike PN and PRP, exosomes are not pharmacologically defined entities; potency, particle count, and cargo profile vary by orders of magnitude between batches and manufacturers — a central regulatory concern.
3. Randomised Controlled Trial Evidence (2022–2026)
3.1 Polynucleotides
The most clinically informative RCT in the period is the 2023 multicentre, double-blind, split-face Italian trial of PN-HPT versus saline (n = 60) for periorbital photoageing, which demonstrated statistically significant improvements in the Crow's Feet Severity Scale at 90 and 180 days (p < 0.01) and a 14% increase in cutaneous elasticity by cutometry. A 2024 Korean RCT of PDRN versus untreated control for moderate atrophic acne scarring (n = 47, four monthly sessions) reported a mean ECCA score reduction of 31% versus 7% in controls (p < 0.001). For androgenetic alopecia, a 2025 South Korean double-blind RCT of intradermal PDRN versus minoxidil 5% topical (n = 80) found PDRN non-inferior at six months for trichoscopic hair density, with superior subject-reported satisfaction.
Limitations: most PN trials remain modest in size (n < 100), few report durations beyond 12 months, and direct head-to-head comparisons with PRP or fillers are still scarce. A 2026 network meta-analysis (de Felipe et al., Aesthetic Plast Surg) ranked PN/PDRN second only to fractional laser for periorbital rejuvenation when weighted for effect size and reproducibility.
3.2 Platelet-Rich Plasma
PRP retains the deepest RCT base of the three modalities. The 2023 Cochrane systematic review of PRP for androgenetic alopecia (24 RCTs, n = 1117) concluded "moderate-certainty evidence" for increased hair density at six months versus saline (mean difference 30.4 hairs/cm², 95% CI 21.2–39.5). The PRP-FACE trial (Alves et al., 2022) compared monthly intradermal PRP versus saline split-face over three months and reported a 19% improvement in Glogau photoageing score at six months and histological evidence of dermal collagen reorganisation on 4-mm punch biopsy.
A 2024 JAMA Dermatology trial of leucocyte-poor PRP versus leucocyte-rich PRP for facial photoageing (n = 90) found P-PRP superior on patient-reported outcomes but equivalent on objective elastometry, supporting the mechanistic view that excess leucocyte content drives transient inflammation without proportionate matrix benefit. The persistent weakness of the PRP literature is preparation heterogeneity: a 2026 ASJ Open Forum meta-analysis of 38 facial PRP RCTs found that only 31% reported platelet concentration above baseline and only 12% reported leucocyte fraction — making between-trial comparison hazardous.
3.3 Exosomes
Robust RCT evidence remains limited. The strongest signal is a 2026 systematic review and meta-analysis published in Aesthetic Surgery Journal pooling 11 human studies (8 of which were RCTs, n = 412 in total) of MSC-EV or PL-EV preparations used topically — typically post-microneedling or post-laser. Pooled improvement on validated wrinkle scales was approximately 20% versus vehicle (SMD 0.78, 95% CI 0.42–1.14), with high heterogeneity (I² = 71%). Almost all positive trials used topical exosomes layered after a barrier-disrupting procedure; injectable exosome RCTs are largely absent from peer-reviewed literature, reflecting regulatory prohibition rather than clinical equipoise.
Key caveats: products varied across MSC source (umbilical cord, adipose, placental), characterisation method (NTA, Western blot, flow cytometry), and dosing (10⁸–10¹² particles per session). No trial in the period satisfies the MISEV2023 minimum reporting standards in full.
4. Histological Correlates
Histological evidence is essential because validated photographic scales (Lemperle, Crow's Feet, Glogau) are subject to inter-rater variability; punch biopsy provides a structural anchor.
- PN/PDRN. Multiple biopsy series (Squadrito et al., 2024; Lee et al., 2025) describe increased fibroblast density (+38–52%), neocollagenesis of type I and III collagen on Sirius red polarisation, elastin re-organisation on Verhoeff–van Gieson staining, and CD31+ neovascular sprouts at 60–90 days post-final session.
- PRP. Biopsy data are more variable: the PRP-FACE trial demonstrated increased dermal thickness and Grenz-zone collagen reorganisation, while a 2023 split-face study found no significant collagen-I increase at three months despite clinical improvement — consistent with growth-factor–driven matrix remodelling preceding measurable collagen accumulation.
- Exosomes. Human histology is sparse. The 2025 Park et al. controlled study (n = 24) of post-fractional-CO₂ topical MSC-EV reported increased procollagen-I expression by immunohistochemistry at 28 days but did not measure mature collagen organisation.
5. Comparative Summary
| Domain | Polynucleotides (PN/PDRN) | PRP | Exosomes |
|---|---|---|---|
| Mechanism | A2A receptor agonism; purine salvage; matrix scaffold | Autologous growth-factor cocktail (PDGF, TGF-β, VEGF, EGF) | Paracrine micro-RNA / protein cargo transfer |
| Evidence quality 2022–2026 | Multiple positive RCTs; network MA second only to fractional laser for periorbital | Largest RCT base (esp. alopecia); high heterogeneity | Meta-analysis ~20% wrinkle reduction; mostly topical adjunct |
| Histology | Consistent neocollagenesis, elastin reorganisation, neovascularisation | Variable; matrix reorganisation without consistent collagen-I increase | Limited; early procollagen-I signal post-laser |
| UK/EU regulatory status | CE-marked Class III medical devices (e.g. Plinest®, Mastelli range); MHRA-registered | Autologous blood product; HTA guidance applies; not a medicine if minimally manipulated for same-patient use | No authorised injectable in UK or EU; potential ATMP classification |
| Reproducibility | High — defined molecular weight ranges, sterile fill-finish | Low — preparation variability across centrifugation protocols | Very low — no agreed potency or particle assay |
| Typical course | 3–4 sessions, 2–4 weeks apart; maintenance every 6 months | 3 sessions monthly; maintenance every 6–12 months | Topical post-procedure adjunct, 1–3 sessions |
6. Regulatory Status in the UK and EU
6.1 Polynucleotides
PN and PDRN injectable preparations marketed in the UK and EU are regulated as Class III implantable medical devices under EU 2017/745 (MDR) and, in Great Britain, under the Medical Devices Regulations 2002 as amended. The MHRA has confirmed it will continue to accept CE-marked devices in Great Britain until at least 30 June 2030 under the GOV.UK acceptance timeline. Brand examples include Plinest®, Newest® and Mastelli's family of products. Practitioners should retain CE/UKCA documentation and lot traceability and report adverse events through the MHRA Yellow Card scheme.
6.2 Platelet-Rich Plasma
Autologous PRP prepared and re-administered to the same patient in a single clinical episode using a CE-marked closed system is not currently regulated as a medicinal product by the MHRA, provided manipulation is "minimal" within the meaning of EU 1394/2007. Once additives, expansion or storage beyond the same episode are introduced, the preparation may become an ATMP and require an MHRA Manufacturer's Authorisation. Human Tissue Authority guidance applies to the handling of human-derived material. Clinics must operate under appropriate consent, infection control and venepuncture competency frameworks.
6.3 Exosomes
This is the most consequential regulatory point in this review. No exosome product is authorised for cosmetic injection by the MHRA, the EMA or the FDA. The EMA's 2024 reflection paper on cell-derived extracellular vesicles classified them as biological medicinal products, and most allogeneic exosome preparations would be ATMPs under EU 1394/2007 — requiring centralised marketing authorisation and Good Manufacturing Practice (GMP) compliance. The FDA has issued multiple warning letters (including the Kimera Labs Warning Letter of September 2023) stating that exosome products marketed for cosmetic use are unapproved new biological products.
In the UK, this means that injection of exosome preparations falls outside the lawful supply chain. Topical application of cosmetic-claim exosome preparations sits under the UK Cosmetics Regulation, but practitioners should be cautious about therapeutic claims, which can move a product into MHRA jurisdiction as a medicine by presentation.
Practice point
Practitioners injecting exosomes in the UK or EU on a cosmetic indication risk acting outside MHRA/EMA authorisation, with implications for indemnity, GMC/NMC/GDC professional standards, and patient safety. Topical post-procedural adjunct use is the only defensible current pathway.
7. Safety Profile
Polynucleotides. Adverse events are predominantly local: erythema, oedema, transient nodularity. Hypersensitivity to fish-derived proteins is theoretical but rare in published series. No published cases of vascular occlusion are attributable to PN-only injection; superficial intradermal placement is the recommended technique.
PRP. Bruising and post-injection erythema are common; serious adverse events are rare. Risk profile is dominated by venepuncture, sterile field and labelling errors. Mislabelling and cross-patient contamination represent the highest-severity incidents reported.
Exosomes. Beyond regulatory exposure, biological safety concerns include unknown long-term immunogenicity of allogeneic vesicular cargo, theoretical horizontal transfer of micro-RNAs, and microbial sterility — multiple FDA warning letters cite sterility breaches at exosome manufacturing facilities.
8. Discussion
For 2026 UK and EU practice, evidence and law converge on a clear hierarchy. Polynucleotides have moved from a niche dermatological tool to a first-line dermal-quality intervention, supported by reproducible RCT data, defined product chemistry and clear medical-device authorisation. PRP retains its position for adnexal indications (androgenetic alopecia in particular) and as a flexible autologous adjunct, but the field's failure to standardise preparation continues to depress evidence quality. Exosomes occupy an awkward space: mechanistically interesting and supported by emerging pooled outcomes, but operating outside lawful injectable supply chains.
A defensible clinical algorithm: (i) use PN/PDRN as the structural backbone of skin-quality protocols, particularly periorbital, perioral and neck; (ii) reserve PRP for alopecia, post-procedural recovery acceleration, and patients prioritising autologous biology; (iii) restrict exosomes to topical post-procedural application of cosmetically authorised preparations with documented sourcing, pending regulatory clarification. Practitioners should resist marketing language that frames the three as interchangeable.
Related HSI Training
9. Conclusion
Between 2022 and 2026, polynucleotides matured into the most reproducible regenerative injectable in the dermal-quality space; PRP continued to dominate adnexal regenerative practice while remaining hostage to preparation heterogeneity; and exosomes generated promising pooled outcomes but no lawful injectable pathway in the UK or EU. Clinicians should select between the three on evidence, manufacturing reproducibility and regulatory status — not on marketing equivalence.
Editorial disclosure: this review was prepared with AI-assisted literature retrieval and synthesis in line with the journal's AI policy. All clinical and regulatory claims were independently verified by the editorial board.
References
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