Trouble at t' (review) mill: How MDPI lets down authors

 I guess many readers will have had peer reviews where the reviewer doesn't appear to have understood, or even properly read, the paper they are criticising. But I doubt that you'll have experienced anything like the authors of this article. Their growing exasperation with increasingly irrelevant comments can be sensed in their response to reviewer 2, who asked them to revise statements that were unproblematic, to add information already in the article, to correct information that was not in the article, and to add two references that bore no relationship whatever to the topic of the article.

So, how can this happen? Well, all becomes plain when you read this article by Maria Ángeles Oviedo-García (2024), who has documented what she terms "review mills": groups of reviewers who generate boilerplate peer reviews that do not evaluate the content of the article, and so can be applied to almost any field. Their main function appears to be to act as citation vehicles for members of the review mill, who encourage authors to "improve" their article with "latest literature", with references to papers by themselves or confederates.

When you see numerous reviews by the same set of people side by side, the boilerplate nature of the reviews becomes obvious, with the same phrases repeated across completely different contexts, e.g.: 

1. The title of the manuscript is not impressive so rewrite the title. 
2. In the abstract, the author should add more scientific findings. 
3. Keywords: There are so many keywords in this manuscript and reduce it. So, modify the keywords. 
4. In the introduction part, the introduction part is not well organized and cited references should cite recently published articles such as 10.3390/toxics10110657, 10.1016/j.rinp.2022.105817

Oviedo-García meticulously documented the evidence for review mill activity on PubPeer, and on 13 February 2024, MDPI's communications department wrote a report outlining how they planned to deal with the situation, noting "MDPI is committed to transparency and integrity in scholarly publishing. We will provide updates as the investigation progresses and appreciate your understanding and cooperation in addressing this matter." 

Neither Oviedo-García nor I have heard of any update to the report, and so in an idle moment I thought it would be interesting to revisit the list of 84 papers to see if anything had been done in the 17 months since that statement. A manual check on 18-20th July 2025, revealed that 46 articles had no action, 13 had a “Journal notice”, stating that they were being looked at, two had the “Review Reports” tab deleted on the website, and the remaining 23 had a Correction. I have added information about Notices and Corrections to PubPeer.

The cases of Correction reveal a lack of consistency in how matters have been handled. The most popular option has been to just delete the peer review from the review mill from the website. The Correction is at explicit that this has been done, but it can be confusing because it often leads to some renumbering of reviews, making it hard to track earlier PubPeer comments against what is online. The other thing that is usually done with the Correction is to remove the coerced references from the article.

Serious problems arise, however, if there were only two original reviews, because MDPI's procedures specify that two reviews are needed; hence, if one has been deleted as improper, they have to seek another review. No doubt the editor fervently hopes that the replacement review will not raise new issues, and sometimes that was the case, but there are instances where the new reviewer wanted substantial changes to the article.

This then creates a most unfortunate circumstance for all concerned. Authors, who thought their article was accepted two or three years previously, are now told that the review process was corrupted, and are expected to revise the article in light of a new review. As far as I can tell from what is publicly on the record, a few authors agreed to do that, but others did not. If it happened to me, I'd be incandescent.

I've only looked at 84 articles from one review mill, but Oviedo-García has documented many more examples, nearly all from MDPI journals, and she suggests urgent actions that publishers should take: be vigilant for fraudulent and plagiarised peer review, blacklist review millers, and develop guidelines for publishers to follow in this situation. Until this is done, authors should be aware that their published article could be slapped with a "Journal notice" expressing concern about the review process, and they could be asked for revisions, even when they are entirely innocent of any wrongdoing.

Reference

Oviedo-García, M. Á. (2024). The review mills, not just (self-)plagiarism in review reports, but a step further. Scientometrics. https://doi.org/10.1007/s11192-024-05125-w