PARIS — A European rule requiring restaurants, bakeries and supermarkets – or anyone mass-producing meals – to list any of 14 allergens that might appear on their menus is being met with confusion.

Italy and France, with their strong restaurant and cafe culture, had yet to outline how the rule approved three years ago should be put into effect. With constantly changing menus, cooks in both countries said communication with the customer – not more rules – was key to a good meal.

Beatrix Chiusole, a diner in Rome, paused as the steam rose from her cheese-topped minestrone to ponder the EU rule. Listing every ingredient of everything on the menu “would be a little off-putting” when perusing menus, she said, adding that she herself had no food allergies. “All you need to do is ask the waiter,” Chiusole said.

Often ingredients that might cause allergy sufferers problems cannot be seen, like the celery simmered into the tomato sauce that is ladled onto spaghetti.

Jean Terlon, owner of Saint-Pierre in Longjumeau, outside Paris, said he relies on customers to tell him about allergies and can easily change recipes to accommodate them.

“We didn’t wait for Europe to be able to tell customers about allergens if they ask,” he said. “There’s no need for a directive.”

But he acknowledged that the increasing number of restaurants that rely on pre-packaged industrial food have less leeway – and know far less about the ingredients on their menus.

In Britain, where the food safety agency made prominent mention of the requirement in effect Saturday, some described it as a simple change that would make life easier for allergy sufferers. Sainsburys, a British supermarket chain, noted: “we are required to change our allergy labelling and allergy advice boxes.”