What is self-plagiarism in research, and when is reuse allowed?
Short answer: self-plagiarism is presenting your own earlier work as new without saying so — most seriously, publishing the same findings twice. Reusing some of your own wording is not automatically wrong: methods descriptions are commonly recycled, and theses routinely become papers. What makes reuse acceptable is transparency (cite the earlier work and tell the editor), new contribution (the paper must add something), and permission where someone else holds the copyright.
The forms it takes
- Duplicate (redundant) publication: the same study, data and conclusions published in two journals, or the same paper submitted to two journals at once. This is the serious form and can lead to retraction.
- Text recycling: reusing passages from your own earlier paper — the introduction, literature review or methods — in a new one.
- Salami slicing: splitting one study into several thin papers that each report part of the same data.
- Undisclosed extension: publishing an extended conference paper as a journal article without saying that the conference version exists.
When reusing your own text is acceptable
- Methods: describing the same protocol in the same words is often clearer than paraphrasing it. Cite the earlier paper; many journals accept this.
- A thesis or dissertation turned into papers: most publishers do not treat a thesis as prior publication. Say in the cover letter that the paper is based on your thesis.
- Preprints: most journals accept submissions that were posted as preprints, for example on arXiv or bioRxiv. Check the journal's preprint policy and link the preprint.
- Conference paper extended into a journal article: usually allowed when the journal version adds substantial new material and the submission states what is new.
Copyright matters too
If you transferred copyright to a publisher, the published wording belongs to them, and reusing long passages may need their permission even though you wrote it. Open-access articles under a CC BY licence can be reused with attribution. Your own thesis is usually yours to reuse, subject to your university's rules.
How editors find it
Journals run submissions through similarity checkers that include published articles — so a recycled introduction shows up as a match against your own earlier paper. A high match to your own work is not proof of misconduct, but an undisclosed one invites questions. Many editors follow the COPE flowcharts on redundant publication and text recycling when they decide what to do.
How to reuse your own work safely
- Cite your earlier publication wherever you reuse its text, data or figures.
- Tell the editor in the cover letter about related papers, the thesis or the conference version, and what is new.
- Rewrite the introduction and discussion for the new paper — they should argue for this paper's contribution, not the last one's.
- Keep reused methods text clearly attributed, and shorten it where you can refer to the earlier paper instead.
- Check the copyright and licence of the earlier publication before reusing figures or long passages.
- Run a similarity check before submission so you see what the editor will see — the plagiarism checker leaves your own earlier checks out of the comparison, so a revised draft is not flagged against itself.
If you need to recast reused passages, the paraphrasing tool keeps technical terms and citations intact; read how to reduce similarity for when rewording is and is not the right fix.