Official statement
What you need to understand
Lazy loading (deferred loading) is a technique that delays image loading until they are close to the user's viewport. While this practice is excellent for optimizing overall site speed, it becomes counterproductive for critical images located above the fold.
Google warns against this common mistake because it directly impacts the Largest Contentful Paint (LCP), one of the most important Core Web Vitals. LCP measures the time required to display the largest visible element in the immediately visible area, often a hero image or main banner.
When you apply lazy loading to these main images, the browser waits for JavaScript to execute before starting the download. This artificial delay degrades user experience and penalizes your performance score, when these images should be loaded with absolute priority.
- Lazy loading is beneficial only for content below the fold
- Hero images and main banners should use standard loading or even be preloaded
- Search Console allows you to verify that your critical images have accessible URLs in the rendered HTML
- The impact on LCP can shift your page from a "good" score to "needs improvement"
SEO Expert opinion
This recommendation is perfectly consistent with what we've been observing in the field since the introduction of Core Web Vitals. Many sites have seen their LCP degrade after implementing lazy loading too aggressively, particularly through WordPress plugins that apply this technique indiscriminately.
However, you need to nuance according to page type. On a homepage with an image carousel, only the first image should be loaded normally, the following ones can be deferred. On e-commerce category pages with numerous products, the first 2-3 visible product rows should escape lazy loading.
loading="eager" attribute or by disabling lazy loading on specific CSS selectors.An often overlooked point: CSS background images in hero sections are not affected by the native loading attribute, but can be delayed by other JavaScript mechanisms. In this case, always favor a classic <img> tag for critical content, possibly combined with a preload in the <head>.
Practical impact and recommendations
- Audit your strategic pages with PageSpeed Insights or WebPageTest to identify the current LCP and verify if it's an image
- Disable lazy loading on all images located in the first screen (generally the first 600-800 pixels)
- Use the loading="eager" attribute explicitly on your hero images to force immediate loading
- Add a preload in the head for your most critical main image:
<link rel="preload" as="image" href="..."> - Configure your plugins (Lazy Load, WP Rocket, etc.) to exclude certain CSS classes or the first X images
- Check in Search Console (Experience > Core Web Vitals section) that your problematic URLs improve after correction
- Test on mobile where LCP is often more critical due to slower connections
- Document your lazy loading strategy to prevent a future update from reintroducing the problem
Optimizing LCP through fine-tuned lazy loading management has become essential for maintaining good SEO performance. This technical issue requires a surgical approach: precisely identify critical images, properly configure tools, and validate the real impact on your Core Web Vitals.
These optimizations affect front-end code, server configuration, and third-party tools, which can quickly become complex depending on your technical stack. For sites with high commercial stakes, working with an SEO agency specialized in web performance allows you to benefit from an in-depth audit and methodical implementation, while avoiding errors that could degrade other aspects of your site.
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