{"id":5052,"date":"2019-07-08T12:13:17","date_gmt":"2019-07-08T12:13:17","guid":{"rendered":"https:\/\/www.24x7wpsupport.com\/blog\/?p=5052"},"modified":"2025-05-02T09:41:56","modified_gmt":"2025-05-02T09:41:56","slug":"how-to-fix-wordpress-cannot-modify-header-error","status":"publish","type":"post","link":"https:\/\/www.24x7wpsupport.com\/blog\/how-to-fix-wordpress-cannot-modify-header-error\/","title":{"rendered":"How To Fix WordPress Cannot Modify Header Error"},"content":{"rendered":"<div class=\"wpb-content-wrapper\"><p class=\"last-updated\">Last updated on May 2nd, 2025 at 09:41 am<\/p><p>[vc_row][vc_column][vc_custom_heading text=&#8221;Introduction&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]Running a WordPress website involves a lot\u2014installing plugins, adding themes, creating pages, and constant editing. But even the smallest changes can sometimes lead to confusing errors. One of the most common and frustrating among them is:<\/p>\n<p><span style=\"color: #ff0000;\"><strong>Warning:<\/strong><\/span> <em><span style=\"color: #0000ff;\"><strong>Cannot modify header information \u2013 headers already sent by (output started at \/path\/to\/file.php:12)<\/strong><\/span><\/em><\/p>\n<p>If you\u2019ve ever encountered the error message \u201cCannot modify header information \u2013 headers already sent by\u2026\u201d while working with WordPress, you\u2019re not alone. This frustrating yet common issue can appear suddenly after editing files, activating a plugin, or even installing a new theme.<\/p>\n<p>In this guide, we\u2019ll break down what this error means, why it happens, and how to fix it step by step \u2014 even if you&#8217;re not a developer.[\/vc_column_text][vc_custom_heading text=&#8221;What Does the Error Mean?&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]This message typically shows up after editing a file, installing a plugin, or switching themes. It means that something (like a space, text, or echo statement) was sent to the browser before WordPress had a chance to send HTTP headers.<\/p>\n<p>Headers in WordPress are essential for redirection, setting cookies, and managing session states. Once the output has started, sending headers isn&#8217;t allowed\u2014which causes this warning.[\/vc_column_text][vc_custom_heading text=&#8221;What Causes the \u201cCannot Modify Header Information\u201d Error?&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]<strong>The error typically looks like this:<\/strong><\/p>\n<p><span style=\"color: #ff0000;\"><strong>Warning:<\/strong><\/span> <em><span style=\"color: #0000ff;\"><strong>Cannot modify header information &#8211; headers already sent by (output started at \/path\/to\/file.php:12)<\/strong><\/span><\/em><\/p>\n<p>It may seem cryptic, but it\u2019s actually pointing you toward the cause \u2014 output was sent before the PHP headers could be modified. In simpler terms, it means that something (like a space, a blank line, or even text) was sent to the browser before WordPress had a chance to send HTTP headers (which are required for things like redirections and cookies).<\/p>\n<p>Here are the most common causes:<\/p>\n<ul>\n<li>Extra whitespace before or after PHP tags (&lt;?php or ?&gt;)<\/li>\n<li>Echo or print statements before header functions like header(), setcookie(), or wp_redirect()<\/li>\n<li>Poorly coded themes or plugins<\/li>\n<li>Files saved with UTF-8 BOM encoding<\/li>\n<li>Manual edits to files like functions.php<\/li>\n<\/ul>\n<p>[\/vc_column_text][vc_custom_heading text=&#8221;Understanding the Error Message&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]Let\u2019s break down an example error message:<\/p>\n<p><span style=\"color: #ff0000;\"><strong>Warning:<\/strong><\/span> <em><span style=\"color: #0000ff;\"><strong>Cannot modify header information &#8211; headers already sent by (output started at \/public_html\/wp-content\/themes\/mytheme\/functions.php:22) in \/public_html\/wp-includes\/pluggable.php on line 1421<\/strong><\/span><\/em><\/p>\n<ul>\n<li><strong>&#8220;output started at&#8230;&#8221;<\/strong>: Tells you where the initial unexpected output started (functions.php line 22).<\/li>\n<li><strong>&#8220;pluggable.php on line 1421&#8221;<\/strong>: Shows the file that attempted to send headers after output had already begun.<\/li>\n<\/ul>\n<p>Always focus on the <strong>first file\/line mentioned<\/strong>, not necessarily the final file where the error was thrown.[\/vc_column_text][vc_custom_heading text=&#8221;Step-by-Step Fixes&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]<\/p>\n<h3>1. <strong>Check for Extra Whitespace<\/strong><\/h3>\n<p>Open the file mentioned in the error (often functions.php, wp-config.php, or a plugin file).<\/p>\n<ul>\n<li>Look for any whitespace (space, blank line, tabs) before &lt;?php at the top or after ?&gt; at the bottom.<\/li>\n<li>Best practice: Avoid closing PHP tags (?&gt;) in files that contain only PHP.<\/li>\n<\/ul>\n<p>\u2705 <strong>Fix<\/strong>:<br \/>\nRemove any space before <strong><span style=\"color: #0000ff;\">&lt;?php or after ?&gt;<\/span><\/strong>. If you see ?&gt; at the end of a PHP file, remove it altogether.<\/p>\n<h3>2. <strong>Use a Proper Code Editor<\/strong><\/h3>\n<p>Some text editors (like Windows Notepad) may automatically insert hidden characters or <strong>UTF-8 BOM (Byte Order Mark)<\/strong> encoding, which can trigger this error.<\/p>\n<p>\u2705 <strong>Fix<\/strong>:<br \/>\nUse a code editor like VS Code, Sublime Text, Notepad++, or PHPStorm.<\/p>\n<ul>\n<li>Ensure files are saved as UTF-8 without BOM.<\/li>\n<li>In Notepad++: Go to Encoding &gt; Convert to UTF-8 (without BOM).<\/li>\n<\/ul>\n<h3>3. <strong>Disable Recently Added Plugins or Themes<\/strong><\/h3>\n<p>If the error appeared after activating a plugin or changing your theme, one of those might be causing output before headers.<\/p>\n<p>\u2705 <strong>Fix<\/strong>:<\/p>\n<ul>\n<li>Use <strong>FTP or File Manager<\/strong> from your hosting panel.<\/li>\n<li>Navigate to wp-content\/plugins and rename the suspected plugin folder (e.g., seo-plugin \u2192 seo-plugin-old).<\/li>\n<li>If it\u2019s a theme issue, switch to a default theme like <strong>Twenty Twenty-Four<\/strong> via the WordPress database or by renaming the current theme folder.<\/li>\n<\/ul>\n<h3>4. <strong>Check the <\/strong>functions.php<strong> File<\/strong><\/h3>\n<p>The functions.php file is especially prone to accidental white space errors or syntax issues.<\/p>\n<p>\u2705 <strong>Fix<\/strong>:<\/p>\n<ul>\n<li>Open functions.php from your active theme.<\/li>\n<li>Review the top and bottom of the file for stray whitespace or blank lines.<\/li>\n<li>Remove any closing PHP tags (?&gt;) if they exist.<\/li>\n<li>Ensure no echo, print, or debug code like var_dump() exists before any header-related code.<\/li>\n<\/ul>\n<h3>5. <strong>Temporarily Use Output Buffering<\/strong><\/h3>\n<p>If you\u2019re unable to quickly find the cause, you can <strong>temporarily suppress the error<\/strong> using output buffering. However, this is a workaround, not a long-term fix.<\/p>\n<p>\u2705\u00a0<strong>Fix<\/strong>: Add this at the top of wp-config.php, just after the opening <span style=\"color: #000000;\">&lt;?php tag:<\/span><\/p>\n<p><em><span style=\"color: #0000ff;\"><strong>ob_start();<\/strong><\/span><\/em><\/p>\n<p>\u26a0\ufe0f Note: This only prevents the warning; it doesn&#8217;t solve the underlying issue.[\/vc_column_text][vc_custom_heading text=&#8221;How to Prevent This Error in the Future?&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]To avoid running into this issue again, follow these best practices:<\/p>\n<h3>Always Use a Quality Code Editor<\/h3>\n<p>Avoid editing WordPress files in plain text editors that can insert invisible characters. Stick to editors that allow you to view and set encoding preferences.<\/p>\n<h3>Don\u2019t Manually Edit Core Files<\/h3>\n<p>Whenever possible, avoid editing WordPress core files or third-party plugin files. Use custom plugins or child themes for your changes.<\/p>\n<h3>Avoid Using ?&gt; at the End of PHP Files<\/h3>\n<p>Many modern WordPress themes and plugins omit the closing PHP tag to prevent accidental whitespace \u2014 and so should you.<\/p>\n<h3>Test Changes on a Staging Site First<\/h3>\n<p>Use a <strong>staging site<\/strong> to test changes before applying them to your live website. This helps catch and fix issues in a safe environment.<\/p>\n<h3>Back Up Before Making Changes<\/h3>\n<p>Always back up your site (especially the wp-content and database) before editing theme or plugin files.[\/vc_column_text][vc_custom_heading text=&#8221;Useful Tools and Resources&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]<\/p>\n<ul>\n<li><strong>Notepad++<\/strong>: Great for removing BOM and managing encoding.<\/li>\n<li><strong>VS Code<\/strong>: Lightweight and feature-rich code editor.<\/li>\n<li><strong>Google Chrome Developer Tools<\/strong>: Useful for identifying front-end issues caused by broken redirections.<\/li>\n<li><strong>WP Debugging Plugin<\/strong>: Helps log errors in a structured format.<\/li>\n<li><strong>WP Staging Plugin<\/strong>: Easily clone your site for safe testing.<\/li>\n<\/ul>\n<p>[\/vc_column_text][\/vc_column][\/vc_row][vc_row][vc_column][vc_custom_heading text=&#8221;Final Thoughts&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]The \u201c<strong>Cannot modify header information<\/strong> \u2013 headers already sent\u201d error is one of the more confusing WordPress errors for site owners, especially when it appears after a seemingly small change. But as you\u2019ve seen, it usually has a straightforward fix, most often caused by whitespace or improper encoding.<\/p>\n<p>Start by checking the file and line number mentioned in the error message. Then, inspect the file for extra spaces or unintended output. Using a proper code editor and following clean coding practices will save you from this error in the future.<\/p>\n<p>If you\u2019re ever unsure, it\u2019s always safer to seek help from an experienced developer or use professional WordPress support.[\/vc_column_text][vc_custom_heading text=&#8221;Need Help Fixing This Error?&#8221; font_container=&#8221;tag:h3|text_align:left&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]If you&#8217;re still stuck or don\u2019t feel comfortable editing code, we can help!<br \/>\n\u2705 Visit our <strong>Live Chat Support<\/strong>: <a href=\"https:\/\/www.24x7wpsupport.com\/\">https:\/\/www.24x7wpsupport.com\/<\/a><br \/>\n\ud83d\udcde Call us:<\/p>\n<ul>\n<li>US &amp; Canada: <strong>+1 888-818-9916<\/strong><\/li>\n<li>UK: <strong>800-069-8778<\/strong><\/li>\n<li>Australia: <strong>1800-990-217<\/strong><\/li>\n<\/ul>\n<p>Let our experts handle the issue for you quickly and safely![\/vc_column_text][\/vc_column][\/vc_row]<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Last updated on May 2nd, 2025 at 09:41 am[vc_row][vc_column][vc_custom_heading text=&#8221;Introduction&#8221; use_theme_fonts=&#8221;yes&#8221; css=&#8221;&#8221;][vc_column_text css=&#8221;&#8221;]Running a WordPress website involves a lot\u2014installing plugins, &#8230;<\/p>\n","protected":false},"author":1,"featured_media":13782,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[350],"tags":[700,701,702,699],"class_list":["post-5052","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-how-to-wordpress","tag-header-error","tag-modify-header","tag-php-header-error","tag-wordpress-header"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How To Fix WordPress Cannot Modify Header Error - 24x7wpsupport<\/title>\n<meta name=\"description\" content=\"In this blog we will help you to understand, how to fix WordPress cannot modify header error. 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Due to the extra empty spaces the PHP header error occurs, which should not be there in your files.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.24x7wpsupport.com\/blog\/how-to-fix-wordpress-cannot-modify-header-error\/\" \/>\n<meta property=\"og:site_name\" content=\"24x7WPSupport Blog\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/24x7wpsupport\" \/>\n<meta property=\"article:published_time\" content=\"2019-07-08T12:13:17+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-05-02T09:41:56+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.24x7wpsupport.com\/blog\/wp-content\/uploads\/2019\/07\/how-to-fix-wordpress-cannot-modify-header-error-1.png\" \/>\n\t<meta property=\"og:image:width\" content=\"825\" \/>\n\t<meta property=\"og:image:height\" content=\"460\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Brian\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@wpsupport24x7\" \/>\n<meta name=\"twitter:site\" content=\"@wpsupport24x7\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Brian\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"7 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/\"},\"author\":{\"name\":\"Brian\",\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/#\\\/schema\\\/person\\\/40ee989d8d57096afc53a526d6e612b0\"},\"headline\":\"How To Fix WordPress Cannot Modify Header Error\",\"datePublished\":\"2019-07-08T12:13:17+00:00\",\"dateModified\":\"2025-05-02T09:41:56+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/\"},\"wordCount\":1322,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/#organization\"},\"image\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/wp-content\\\/uploads\\\/2019\\\/07\\\/how-to-fix-wordpress-cannot-modify-header-error-1.png\",\"keywords\":[\"Header Error\",\"Modify Header\",\"PHP Header Error\",\"WordPress Header\"],\"articleSection\":[\"How To Wordpress\"],\"inLanguage\":\"en-GB\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/\",\"url\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/\",\"name\":\"How To Fix WordPress Cannot Modify Header Error - 24x7wpsupport\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/how-to-fix-wordpress-cannot-modify-header-error\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/www.24x7wpsupport.com\\\/blog\\\/wp-content\\\/uploads\\\/2019\\\/07\\\/how-to-fix-wordpress-cannot-modify-header-error-1.png\",\"datePublished\":\"2019-07-08T12:13:17+00:00\",\"dateModified\":\"2025-05-02T09:41:56+00:00\",\"description\":\"In this blog we will help you to understand, how to fix WordPress cannot modify header error. 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