What punctuation mark should be used to separate three or more items in a series when any of the items already contain commas?

When dealing with a series of items that already contain commas, the use of a semi-colon is essential for clarity. This is because a semi-colon effectively separates items, reducing the potential for confusion that can arise when multiple commas are present. For example, in a list such as "apples, oranges, and bananas, which are all ripe; carrots, celery, and bell peppers, which are fresh; and milk, cheese, and yogurt, which are dairy products," the semi-colons delineate the groups clearly.

In contrast, employing just commas among such items could lead to misinterpretation, as one might struggle to determine which items belong together. Thus, the semi-colon serves as a strong visual cue that helps maintain the integrity of the divided segments in the list. This use of punctuation enhances readability and ensures that the intended grouping is unmistakable, making the written communication much clearer and more professional.