Redirects are an important technique for getting website visitors to the appropriate Web page if it has moved, but they can negatively impact SEO if implemented poorly. Because spammers have misused some redirect techniques, search engines may penalize your website for using them. Instead, most experts advise using the 301 permanent redirect to best maintain the Web page's reputation for SEO purposes.
Importance of Page Reputation
Pages that accumulate lots of links from quality websites are deemed reputable by search engines. SEO can be impacted by redirects in negative ways if the page's reputation, or PageRank in Google's terms, is not passed along to the new page. However, redirects can also increase a page's reputation by passing along the so-called "link juice" of duplicate pages to a single destination.
Poor Redirect Methods
Meta refresh and 302 temporary redirects are two types of redirect methods that negatively impact SEO. A meta refresh is performed by inserting a simple snippet of code into a Web page's metadata to automatically redirect visitors to another page. This method is easily abused by spammers, so many search engines penalize Web pages that use meta refresh redirects.
A 302 is a server-side redirect that is included in a website's ".htaccess" file and indicates that a Web page has been found or moved temporarily. Few search engines pass the page's reputation to a new page if a 302 redirect is used, resulting in a new page that may rank lower in search results than its predecessor.
301 Permanent Redirects
Permanent redirects are the preferred method for redirecting Web pages in regards to search engine optimization concerns. Like temporary redirects, permanent redirects are a server-side redirect issued via the ".htaccess" file. However, most search engines pass the Web page's reputation to the new page when a permanent redirect is used. The search engine soon recognizes the new page as the replacement for the old, and damage to the page's search placement is minimized.
Using Redirects to Improve SEO for Duplicate Content
Duplicate content, or Web pages with very similar information, is disliked by search engines because it is often an attempt to gain extra visitors by unscrupulous means. As your website evolves, you may realize that some of your pages are duplicates. Redirecting the duplicates to a single page can positively impact your search rankings. In addition to avoiding penalties, combining the power of each page's reputation into a single optimized page will often result in better search placement.