If the content is too old (older than its freshness lifetime), it is considered stale. An HTTP cache should contact the origin server and check whether the content is still fresh before serving stale content to a client. The origin server will either respond with replacement content if not still valid, or ideally, the origin server will respond with a code to tell the cache the content is still fresh, without the need to generate or send the content again. The content becomes fresh again and the cycle continues.