The Unwanted Borders
Google Docs often attempts to apply consistent formatting across an entire document. A frustrating scenario occurs when you are working with headers. If you double-click into the header section (the space at the very top of the page above the margin) and type a title, you might decide to add a horizontal line beneath it using the paragraph border tool to make it look professional. However, if you then click back into the main body of the document and hit Enter, Google Docs sometimes automatically inserts that same horizontal header line onto every new paragraph you create, assuming you want a continuous bordered theme.
Breaking the Border Cycle
To stop Google Docs from automatically inserting header lines into the main body of your document, you must explicitly clear the formatting or adjust the paragraph borders directly.
If you notice the line appearing immediately after hitting Enter, the fastest solution is to break the formatting chain. Before typing anything on the new line, press Ctrl+\ (backslash) on Windows/ChromeOS or Cmd+\ on macOS. This strips the inherited border formatting. If you already have several paragraphs with unwanted lines, highlight the affected text in the main body. Go to the primary menu bar, click on Format, hover over Paragraph & spacing, and select Borders and shading. A dialogue box will appear. You will likely see the “Bottom border” icon highlighted in blue. Click that icon to deselect it, ensure the “Border width” is set to 0 pt, and click Apply. This removes the lines from your body text without affecting the design you created in the actual header section.