What causes the “Headers Already Sent” error?

The "Warning: cannot modify header information - headers already sent by" issue You'll see this message if a PHP file cannot be executed because of a problem in its code.

If there is an issue within one of the .php files that your website needs to load, This is how the error message will appear to you:

• Warning: Cannot modify header information - headers already sent by (output started at /home/public_html/wp-config.php:#) in /home/public_html/wp-content/plugins/my-plugin/function.php on line 28

How to troubleshoot and fix the "Headers Already Sent" error in WordPress?

Method - 1: Fix the "Headers Already Sent" error - using plugin/themes

1. Login to your WordPress Dashboard.
2. Scroll down to Appearance > Theme File Editor.

3. Select the function.php file.

You will see several whitespaces before the <?php tag or after the closing ?> tag and the file’s last line of code; those whitespaces are the problem.

To solve this error, remove all the whitespaces and click the Update File button.




You can execute the same procedure using the WordPress plugin editor (Plugins > Plugin Editor). This approach is appropriate if the error message mentions a corrupt plugin file.


Method - 2: Fix the "Headers Already Sent" error - using CPanel

1. Log into your CPanel account.
2. Scroll down to the Files and choose File Manager.

3. Inside the public_html directory, select the wp-config.php file.
4. Right-click on the wp-config.php file and select Edit.




Once a file is open, find the issue by scrolling to the line the error message directed you toward.

You should get guidance from someone with knowledge of working with PHP files if you cannot identify the error. But let's say you need help with whitespace or a sentence that comes before the PHP header. In that scenario, you should be able to resolve the issue independently.