An Expression of Concern is published when serious doubts have been raised about an article but the evidence is not yet conclusive; for example, while an institutional investigation is ongoing or when the authors cannot be reached.

• The notice is linked to the article and explains the nature of the concern.
• It is updated or replaced by a correction or retraction once the matter is resolved.
• If the concern is dismissed, a note is added stating that the issue has been resolved.