Recently, in a Google Webmaster Hangout, John Mueller answered a query that would using the same content for product and category pages demote or affect any one or both the pages. He threw light on how Google handles duplication of content among product and category pages, the consequences of repeating snippets, and puts forward his opinion on how publishers should handle this.
Category pages consist product listings, which users can browse through and click on a specific product. They will be then redirected to the product page. The problem arises when these two contain the same content.