Having pages being reachable from multiple URL's could harm your rankings, so it's best to prevent this. This can be done in many different ways. Some can be used on their own, but you can also combine techniques to totally get rid of your duplicate. In prestashop, there are great ways of using modules and for this "Duplicate URL Redirect" is one of the module to prevent this and it is an invaluable SEO tool you can get for your shop!
The module will : Redirect all duplicate, deleted, invalid and non- SEO friendly URLs to the default Friendly URL.
Available at : http://www.prestades...e-url-redirect/
