How to show categories for post with commas if more than one category?

<?php
     $categories = get_the_category();
     foreach ($categories as $category){
     echo $category->cat_name;}
?>

Currently this will display categories as "cat1cat2cat3" What I want it to be is "cat1, cat2, cat3"

I tried this echo $category->cat_name . ', '; but this just adds a comma after every category. Even if the post just has one category: Ex. "cat1, " And it also adds commas to the last category in the list: Ex. "cat1, cat2, cat3, "

So how can I get the commmas in but absent if just one category and absent on the last category if its a list?