Thin Mints are the best-selling Girl Scout cookies. They account for a quarter of all cookie sales, according to the Girl Scouts of the United States of America.

You might expect all Thin Mint cookies are the same. But that's not true.

Most Thin Mint fans probably don't care that there actually are two versions of the cookie. The ingredients are nearly identical.

For vegans or people with milk allergies, it's pays to take a close look at the nutrition and ingredient section of the Thin Mint box.

Some Thin Mints are produced by Little Brownie Bakers, which is owned by Kellogg Company. Those cookies contain whey, which is a milk ingredient.

The other variety of Thin Mints are made by ABC Bakers, which is part of Interbake Foods. That version contains no milk ingredients, so they're labeled "vegan."

The ABC Bakers Thin Mints contain high fructose corn syrup, while the label for the Little Brownie Bakers version doesn't mention HFCS.

A close look at the "nutrition facts" of the two Thin Mint versions reveals slight differences in the amount of fat, sodium, protein and iron.

There's no explanation on the Girl Scouts website as to why the two bakers aren't required to use identical ingredients when they produce Thin Mints so the cookies sold across the United States would be the same.

Some Thin Mint lovers wind up going online to seek out cookies that don't contain milk ingredients if that version isn't available from Girl Scouts in their area.