When I was working on foodjumper, there were times when I wanted to check the parent category, for example, if you’re in the Dinner category or viewing a post in that category, I want to display the proper layout for posts in the Recipes category. One function that works, is to do a check like this:

function parent_category( $cats, $_post = null ){
    if( is_string($cats) )  $cats = get_cat_ID($cats);
    foreach ( (array) $cats as $cat ) {
        $descendants = get_term_children( (int) $cat, 'category');
        if ( $descendants && in_category( $descendants, $_id ) ) return true;
    return false;

WordPress published a similar function on their site, but it used the actual category ID in the function. I found it easier to let you enter the slug instead. Now, when you want to check if a post is in a category that is a child, you can do a check like this:

if(in_category('recipes') || parent_category('recipes') ): 
    // display this post as a recipe
    // display this post as a normal post

This can be adapted to almost any type of similar treatment, I just used recipes above as an example since it’s where I just used this function.