A Nature investigation has revealed mounting concerns over the emergence of so-called “review mills”, exposing how duplicated peer-review reports, questionable citation practices and mounting pressures within academic publishing are challenging confidence in one of science’s most important quality-control systems. The investigation highlights the experiences of researchers, publishers and research-integrity specialists as they grapple with a phenomenon that not only threatens the integrity of scholarly publishing but also leaves innocent authors caught in the fallout.
An investigation reported by Nature has cast fresh light on the growing challenge posed by “review mills”, a phenomenon in which duplicated peer-review reports and inappropriate citation requests are increasingly surfacing across academic journals. While concerns over superficial or poor-quality reviews have long existed, the investigation suggests that systematic reuse of reviewer comments and efforts to inflate citation counts are becoming more sophisticated, raising difficult questions about research integrity, editorial oversight and the pressures shaping modern scientific publishing.
For Michael Börsch, a biophysical chemist at Friedrich Schiller University Jena in Germany, the issue became personal in April 2023. After submitting a manuscript examining an enzyme responsible for producing the energy-carrying molecule ATP, Börsch received two peer reviews. One reviewer provided detailed and constructive feedback. The second, however, submitted what Börsch describes as the “laziest peer review” of his three-decade scientific career.
According to Börsch, Reviewer 2 reproduced sections of the manuscript’s abstract before making a series of generic requests, including shortening the conclusion, improving the English grammar and discussing measurements that were not part of the study. The reviewer also recommended citing two unrelated Alzheimer’s disease papers. Börsch rejected those requests while carefully responding to the useful comments from Reviewer 1, and the paper was subsequently published in the International Journal of Molecular Sciences, part of the MDPI publishing portfolio.
Months later, the publication became embroiled in a much larger controversy. In December 2023, Maria Ángeles Oviedo-García of the University of Seville identified reviewer comments strikingly similar to those received by Börsch across dozens of manuscripts. She later documented 263 reviewer reports containing evidence of what she termed “review mills” in a 2024 Scientometrics paper, describing individuals or groups who duplicate reviewer reports, probably to increase citations to their own work or that of collaborators.
Following those findings, MDPI attached a yellow warning notice to dozens of affected papers, including Börsch’s. The notice stated that one reviewer had not adequately assessed the manuscript and that additional peer review was being conducted. Börsch argues that this unfairly undermined research produced through 15 months of work despite no wrongdoing by his team. “We did solid science. We did the review process,” he told Nature, questioning why authors should bear the consequences of failures elsewhere in the publication process.
The investigation suggests that Börsch’s experience reflects a broader problem confronting scholarly publishing. Publishers including Springer Nature, Taylor & Francis and PLoS ONE told Nature that they have observed increasing numbers of reviewer reports containing duplicated language alongside irrelevant citation requests. Analysis presented at the 2025 International Congress on Peer Review and Scientific Publication found that between 0.5% and 1.3% of nearly 150,000 peer-review reports examined were highly similar to others, while Institute of Physics Publishing reported that 0.05% of reviews submitted to its journals in 2025 were completely identical and 0.3% shared at least 80% overlap.
Psychologist Dorothy Bishop, emeritus professor at the University of Oxford, believes the problem could be considerably larger than currently recognised. She argues that increased publication of peer-review reports has made such practices easier to detect, particularly within MDPI journals, while artificial-intelligence tools may also contribute by making it easier to generate generic review content. At the same time, she maintains that greater transparency remains essential because publicly available reviews help expose problematic behaviour.
The investigation also highlights the intense pressures experienced by reviewers. Abd Dagestani, a sustainability researcher at Central South University in Changsha, China, acknowledged reusing portions of reviewer reports after becoming frustrated by what he regarded as an overwhelming volume of review requests and editorial decisions that appeared to disregard detailed reviewer feedback. Although he later said, “I don’t duplicate anything”, Dagestani described how repeated demands on reviewers and a sense of being undervalued encouraged him to provide increasingly generic assessments. MDPI stated that it neither expects nor encourages duplicated reviews and said it values reviewers through fee discounts, awards and formal recognition while also working to identify reviewer cartels.
According to Bishop, the principal motivation behind review mills is often the pursuit of citations, which continue to influence hiring decisions, promotions, university rankings and research funding. The investigation examines allegations involving engineer Rabiul Awual, whose work has accumulated nearly 43,000 Google Scholar citations. Science sleuth Fabian Wittmers argues that excessive self-citation and repeated requests to cite Awual’s work have contributed substantially to those figures. A now-retracted study concerning caesium removal from wastewater cited Awual’s own research 123 times, prompting a retraction notice describing many of those references as having “either borderline relevance or no relevance whatsoever to the article” and characterising the practice as “a violation of publishing ethics”. The authors disputed the grounds for retraction.
Nature also reports allegations that reviewer requests have pressured authors into citing irrelevant studies. One anonymous researcher described feeling compelled to include multiple references to Awual’s work following reviewer comments that implied acceptance might depend upon compliance. Elsevier stated that its policies prohibit reviewers from recommending citations to their own work or that of associates unless scientifically justified and that editors may remove inappropriate citation requests.
The investigation extends beyond individual cases to examine broader citation patterns. Citation maps show how excessive self-citation, reciprocal citation among collaborators and reviewer-suggested references can collectively inflate citation counts. Bishop and Oviedo-García also identified what they describe as a network of at least nine Italian oncologists who allegedly used similar review templates to secure citations across 170 articles, suggesting that some review mills may operate through coordinated groups rather than isolated individuals.
For publishers, responding to such activity presents difficult choices. Springer Nature told Nature that individuals found repeatedly manipulating citation practices can be prevented from reviewing and may face further sanctions, including restrictions on publishing in its journals. PLOS publication ethics head Renee Hoch explained that journals sometimes issue expressions of concern or retract papers when peer-review integrity has been compromised, not as punishment but to maintain confidence in the scientific record.
MDPI maintains that post-publication notices are intended to inform readers transparently rather than penalise authors. The publisher says it has strengthened oversight of peer review since the Scientometrics study and would consider retraction only if an article’s findings were shown to be unreliable. In Börsch’s case, it stated that this threshold had not been met.
Despite those assurances, Börsch remains deeply frustrated. He argues that the burden of correcting failures in peer review has been shifted onto authors whose research was conducted properly. Having abandoned efforts to remove the warning notice attached to his ATP enzyme paper, he says he no longer submits work to MDPI journals. His experience, as reported by Nature, illustrates the difficult position faced by researchers who become entangled in efforts to protect scientific integrity despite having committed no misconduct themselves.
As publishers develop new tools, including duplicate-review detection systems, and continue investigating review-mill networks, the investigation concludes that lasting solutions will require more than technological safeguards. Addressing the underlying pressures driving researchers to duplicate reviews and manipulate citations may prove just as important if confidence in peer review is to be preserved.
