I'm working with a CMS that allows me to post content in to multiple categories.

So, I have this link:

www.site.com/category/green-cars

Here are the GREEN cars
    TITLE: A Big green car
    INTRO: this is a great big green car.

But then I have this link:

www.site.com/category/big-cars

Here are the BIG cars
    TITLE: A Big green car
    INTRO: this is a great big green car.

So essentially - for every item of content, header and the intro sentence is the same regardless of the category the item appears in.

Will a search engine penalise the site for having the same content in this way?

I've looked at canonical links, but I don't think this is relevant here. All my content points to the same page - but the content may appear in multiple categories first.

Or am I worrying about nothing?

Thanks.