It’s easy to confuse the two dressings: they are similar in appearance, and both start with a base of mayonnaise and ketchup.   The difference is in the details. Authentic Thousand Island is on the sweeter side and, surprisingly, includes a hard-boiled egg. Russian dressing is considerably spicier than Thousand Island, taking on some heat with the addition of horseradish, paprika, and red pepper flakes.