What Are Ancient Antimicrobial Peptides and Could They Treat Acne or Skin Infections?

Ancient antimicrobial peptides (AMPs) are short, cationic protein fragments — typically between 5 and 100 amino acids in length — that predate modern medicine by hundreds of millions of years and form the skin's original chemical shield against pathogens. In September 2026, University of Oregon biologists published research in PLOS Biology showing that reconstructed versions of these peptides from mammals that lived 160 million years ago were more potent against drug-resistant bacteria than some of their modern human counterparts — a finding with immediate implications for dermatology, particularly for antibiotic-resistant acne and chronic skin infections.

The timing matters. Antibiotic resistance is accelerating globally, and the skin is one of the first battlegrounds. Understanding how evolution already solved the resistance problem — repeatedly, over geological timescales — gives researchers a blueprint no laboratory could have invented from scratch.

Quick Comparison: Key Antimicrobial Peptides Relevant to Skin Health

AMP	Source	Primary Skin Targets	Resistance Risk	Development Stage
LL-37 (cathelicidin)	Human keratinocytes, neutrophils	C. acnes, S. aureus, P. aeruginosa, E. coli	Low (membrane disruption mechanism)	Clinical trials (derivatives)
hBD-2 (β-defensin)	Human keratinocytes	E. coli, P. aeruginosa, P. acnes, MRSA	Low	Preclinical / early clinical
hBD-3 (β-defensin)	Human keratinocytes	Broad-spectrum incl. MRSA, VRE	Low	Preclinical
RNase 7	Skin epithelium	P. acnes, S. aureus, MRSA, Candida albicans	Low	Research phase
Lactoferricin (ancient reconstructed)	Resurrected from 160 Ma mammal ancestor	S. aureus, P. aeruginosa, E. coli, Streptococcus	Under investigation	Basic research (UO, 2026)
RP556 (designed AMP)	Synthetic / engineered	Multidrug-resistant C. acnes	Very low (engineered)	Preclinical murine model

Sources: Frontiers in Immunology (2024); PMC – Marcinkiewicz & Majewski (2016); PubMed – Woodburn et al. (2020); ScienceDaily / UO (2026)

What exactly are antimicrobial peptides, and where do they come from?

Antimicrobial peptides are small, mostly positively charged (cationic) proteins produced by virtually every living organism — from bacteria and fungi to insects, amphibians, and mammals — as a rapid-response weapon against microbial invaders. In humans, they are found in keratinocytes, eccrine gland cells, mast cells, phagocytes, and sebocytes, making the skin both a producer and a primary deployment site.

Their mechanism is physical rather than biochemical. Because AMPs carry a positive charge and bacterial membranes carry a negative charge, the peptides are electrostatically attracted to pathogens while largely ignoring the neutrally charged membranes of human cells. Once they reach a bacterial membrane, they insert themselves into the lipid bilayer, creating pores that rupture the cell. This membrane-disruption strategy is why bacteria have historically struggled to develop resistance to AMPs — you cannot easily mutate your way out of having a membrane.

The major human AMP families relevant to skin include:

Cathelicidins — the most studied human representative is LL-37, produced in response to inflammation and vitamin D signaling.
Defensins — α-defensins are found mainly in neutrophil granules; β-defensins (hBD-1, hBD-2, hBD-3) are expressed by skin epithelial cells and are inducible by bacterial stimuli.
S100 proteins, including psoriasin (S100A7), which is active against E. coli and P. acnes.
Ribonucleases, particularly RNase 7, which shows antimicrobial activity against P. acnes, S. aureus, MRSA, and Candida albicans.

Beyond killing microbes directly, AMPs also act as immune modulators — recruiting T cells, dendritic cells, and neutrophils to infection sites, promoting wound healing, and influencing the adaptive immune response. This dual role sets them apart from conventional antibiotics, which are purely antimicrobial.

What did the University of Oregon researchers actually discover?

The 2026 University of Oregon study, published in PLOS Biology, used a technique called ancestral sequence reconstruction to rebuild proteins that no longer exist in any living organism. Lead author Titas Sil began by comparing lactoferrin gene sequences from living species — humans, cows, and other placental mammals — then mapped the evolutionary relationships among those sequences and used statistical methods to estimate the most likely genetic sequences carried by their extinct common ancestors, extending the reconstruction back roughly 160 million years to the Jurassic Period.

Lactoferrin is an immune protein present in almost every body fluid except blood — breast milk, tears, saliva, mucus — and its primary job is iron sequestration: it binds iron so tightly that bacteria inside the body cannot access it. Lactoferrin also contains an embedded antimicrobial peptide capable of directly damaging bacterial membranes. Close relatives of lactoferrin lack this ability, which means the trait evolved specifically within the lactoferrin lineage after placental mammals emerged.

Sil synthesized the predicted ancient genes and used cells to produce the reconstructed proteins, then tested them against Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Streptococcus — all pathogens with major roles in skin and wound infections.

The results were unexpected in two ways. The oldest reconstructed peptides (160 million years old) could disrupt bacterial membranes, but bacteria repaired the damage and survived. Versions from more recent mammalian ancestors — dating back only a few million years — were progressively more lethal, and in several cases outperformed the equivalent modern human peptides. The researchers traced much of this enhanced potency to a single amino acid mutation: one change in the chain of protein building blocks was sufficient to dramatically increase killing power.

"What was surprising and unexpected was how small changes in these domains could have such large effects," said senior author Matt Barber. The finding suggests that the evolutionary record contains a rich archive of structural solutions — natural experiments run over millions of years — that could inform the rational design of new antimicrobial drugs.

How do AMPs connect specifically to acne vulgaris?

Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit — the structure comprising the hair follicle, sebaceous gland, and arrector pili muscle — driven by four intersecting factors: androgen-stimulated sebum overproduction, follicular hyperkeratinization, dysbiosis of skin microbiota (particularly Cutibacterium acnes), and immune activation. In 2010, acne ranked in the top 10 most prevalent diseases worldwide, affecting 85% of adolescents in Westernized populations.

AMPs are not bystanders in acne — they are central players. Elevated expression of AMPs including human β-defensins, cathelicidin LL-37, dermcidin, and RNase-7 is a hallmark of acne-affected skin. Researchers now believe this elevated expression represents a compensatory mechanism to protect skin with an impaired permeability barrier — the skin essentially trying to compensate for dysbiosis by ramping up its chemical defenses.

The connection to antibiotic resistance is direct and urgent. Mild acne is typically treated with topical antibiotics; more severe inflammatory forms require prolonged oral antibiotic courses. This prolonged use drives resistance in C. acnes strains, and resistant isolates are now common in clinical settings. Innovative treatment alternatives providing complete microbicidal eradication with minimal safety issues and limited susceptibility to microbial resistance are fervently sought.

LL-37 has demonstrated activity against C. acnes in multiple studies, and its expression is regulated partly by vitamin D — which may partly explain why sunlight exposure has historically been associated with acne improvement, though this relationship is complex and not a basis for sun-seeking behavior. β-defensin hBD-2 is specifically induced by P. acnes (now reclassified as C. acnes) and shows killing activity against the bacterium. RNase 7 is constitutively expressed in healthy skin and serves as a continuous low-level guard against C. acnes colonization.

A 2024 review in Frontiers in Immunology went further, hypothesizing that AMPs also play a role in regulating the tight junctions of the skin barrier by activating cellular proteins including PI3K, GSK-3, aPKC, and Rac1 — linking AMP activity to the metabolic signaling pathways (insulin/IGF-1, mTOR/FoxO1) that are increasingly understood to drive acne pathogenesis in Western dietary contexts.

Are designed or engineered AMPs already being tested for acne treatment?

Yes, and the results from preclinical work are genuinely promising. Researchers at Riptide Bioscience engineered a series of designed antimicrobial peptides (dAMPs) — synthetic analogs of naturally occurring AMPs modified to reduce the likelihood of bacterial resistance. Seven novel sequences were screened against antibiotic-resistant C. acnes clinical isolates, and five peptides (RP444, RP551, RP554, RP556, and RP557) exhibited potent in vitro antibacterial activity.

The lead candidate, RP556, achieved a Therapeutic Index of 130 — meaning it was 130 times more selective for killing multidrug-resistant C. acnes than for harming human keratinocytes. In a murine intradermal infection model, a topical application of just 0.5% RP556 eliminated the infection entirely. The researchers concluded that if these preclinical results translate clinically, dAMPs may become a viable topical monotherapy for recalcitrant acne infections.

This matters because it addresses the core limitation of conventional antibiotics: selectivity. An ideal acne treatment kills C. acnes without damaging surrounding skin cells or disrupting the broader skin microbiome. A Therapeutic Index of 130 suggests RP556 comes close to that profile, at least in laboratory and animal models.

The ancient peptide research from the University of Oregon adds a new dimension to this engineering effort. Rather than designing AMPs purely from scratch, researchers can now mine evolutionary history for structural motifs that evolution already validated over millions of years of pathogen pressure — then use those motifs as starting points for synthetic optimization.

What are the barriers to AMPs becoming actual skin treatments?

The barriers are real and should not be minimized. Barber and Sil explicitly caution that resurrected antimicrobial peptides are unlikely to become new medicines anytime soon. The primary obstacles are:

Structural instability. Unlike small-molecule antibiotics, peptides are chains of amino acids that the body's own proteases rapidly degrade. Applied topically, an AMP may be broken down before it can reach its target in the follicle. Applied systemically, degradation is even faster. This is why most AMP-based drug development focuses on topical delivery or on engineering peptides with modified backbones that resist enzymatic cleavage.

Manufacturing cost and complexity. AMPs are short proteins found in a variety of life forms, and their pharmacological potential has been investigated intensively, but synthesizing them at pharmaceutical scale remains expensive compared to small-molecule drugs. Solid-phase peptide synthesis, the dominant manufacturing method, becomes cost-prohibitive for longer sequences.

Delivery challenges. Getting any active ingredient into the pilosebaceous unit — the anatomical target in acne — requires formulation strategies that overcome the skin barrier. Nanoparticle encapsulation, liposomal carriers, and hydrogel matrices are all being investigated as AMP delivery vehicles, but none has yet achieved regulatory approval for an AMP-based acne product.

Resistance is not impossible. While AMPs are harder to develop resistance against than conventional antibiotics, resistance risk is not zero. Barber acknowledges: "Similar to antibiotics, pathogens are going to be able to evolve against antimicrobial peptides." Some bacteria have evolved mechanisms to modify their membrane charge, produce proteases that degrade AMPs, or pump AMPs out of the cell. The evolutionary data from the UO study may actually help here — by understanding how AMPs changed in response to bacterial counter-evolution over millions of years, researchers may be able to anticipate resistance pathways and design around them.

Regulatory pathway. AMPs occupy an ambiguous regulatory space — they are neither small-molecule drugs nor biologics in the traditional sense. Regulatory agencies in the US and EU are still developing frameworks for peptide therapeutics, which adds time and cost to clinical development.

How do AMPs differ from antibiotics in their approach to bacterial killing?

This distinction is worth understanding clearly because it explains both the promise and the complexity of AMP-based treatments.

Conventional antibiotics typically target a specific bacterial protein or process — a cell wall synthesis enzyme, a ribosomal subunit, a DNA replication mechanism. Because the target is specific, a single mutation in the bacterial gene encoding that target can confer resistance. This is the evolutionary pressure driving the global antibiotic resistance crisis.

AMPs, by contrast, primarily target the physical structure of the bacterial membrane itself. The membrane is not encoded by a single gene — it is a complex lipid bilayer whose composition is constrained by fundamental biophysical requirements. Bacteria cannot easily mutate their way to a membrane that repels AMPs without also compromising their own survival. This is why AMPs can target a broad range of pathogens, and due to their potency, scientists have been trying to synthesize a variety for therapeutic uses.

Many AMPs are also immunomodulatory — they do not just kill bacteria directly but recruit and activate immune cells, promote tissue repair, and modulate inflammatory signaling. An AMP-based treatment for acne might therefore simultaneously address the microbial component (killing C. acnes), the inflammatory component (modulating cytokine release), and the barrier component (promoting tight junction integrity). No single conventional antibiotic achieves all three.

The ancient peptide research adds another layer: by studying how AMPs evolved in response to actual pathogen pressure over 160 million years, researchers gain access to structural solutions that were tested against real bacterial populations, not just laboratory strains — a fundamentally different kind of data than what emerges from rational drug design alone.

What does this mean for people with acne or recurring skin infections right now?

Ancient AMPs are not yet available as treatments. The University of Oregon research is foundational science — it establishes proof of concept that evolutionary reconstruction can yield peptides more potent than current human versions, and it identifies the structural features (including single amino acid changes) that drive that potency. Translating that into a topical gel or cream requires years of additional work.

What is closer to hand is the broader AMP research pipeline. Several lactoferrin derivatives have already entered clinical trials for infection treatment, as noted in the UO study. Designed AMPs like RP556 have shown strong preclinical results against antibiotic-resistant C. acnes. The cosmeceutical industry is also investigating AMPs as potential ingredients in skincare products due to their antioxidant properties and antibacterial activity, which allows the killing of bacteria that contribute to acne and other skin conditions.

For people dealing with antibiotic-resistant acne specifically, the near-term clinical relevance lies in understanding why conventional treatments may be failing. If C. acnes strains have developed resistance to tetracyclines or clindamycin, membrane-disrupting peptides — which work through a different mechanism — could be effective where antibiotics are not. Dermatologists are increasingly aware of this, and the pipeline of AMP-based topical products is advancing.

The immunomodulatory role of AMPs is also relevant to conditions well beyond acne. Several inflammatory skin diseases including psoriasis, atopic dermatitis, acne vulgaris, and rosacea are characterized by a dysregulated expression of AMPs. In psoriasis and rosacea, AMPs are overexpressed; in atopic dermatitis, they are underexpressed. This dysregulation is not just a symptom — it is increasingly understood as a driver of disease progression, which means AMP-modulating therapies could have applications across multiple chronic skin conditions.

For those exploring peptide-based skincare in the interim, products containing amino acid complexes — such as those reviewed in our guide to amino acid scalp shampoos — represent a related but distinct category: they support the skin's structural proteins rather than directly mimicking AMP function. True AMP-based cosmeceuticals remain a developing category, and claims should be evaluated carefully against the underlying research.

What comes next in ancient AMP research?

The University of Oregon team's immediate next steps involve understanding how bacteria evolve resistance to the reconstructed ancient peptides — and whether that resistance pathway differs from resistance to modern human AMPs. If ancient peptides trigger different resistance mechanisms, or if resistance develops more slowly, that information could guide the design of combination treatments that are harder for pathogens to escape.

Barber frames the evolutionary record as a "billions-year-old science experiment" whose results are available for study. The ancestral sequence reconstruction method used in this work — pioneered by Joseph Thornton, a former UO scientist — is now being applied to a growing range of immune proteins, and the lactoferrin study is likely to inspire similar reconstructions of other AMP families including defensins and cathelicidins.

The finding that a single amino acid mutation was sufficient to dramatically enhance antimicrobial potency carries particular weight for drug design. Researchers may not need to engineer entirely novel peptide sequences — they may only need to identify the one or two structural changes that evolution already discovered and incorporate them into existing peptide scaffolds. That is a far more tractable design problem than building a new antibiotic from scratch.

The research was funded by the National Institutes of Health, and the paper is published open-access in PLOS Biology, meaning the full structural data on the reconstructed peptides is available to the broader research community. That accessibility accelerates the translation timeline, even if clinical applications remain years away.

The skin, it turns out, has been running its own antimicrobial research program for 160 million years. Scientists are only now beginning to read the results.