Coumarin

It depends on the use, and food and cosmetics are governed by different rules. As a fragrance ingredient in cosmetics, coumarin is permitted in the EU (not banned), but it must be declared on the label as a recognised fragrance allergen. The "banned" reputation comes from food law: coumarin cannot be added to food as a pure substance, and in the US it is prohibited as a direct food additive.

Coumarin is permitted for use in cosmetics in the EU and is considered acceptable at the low levels used in fragrance, but it is officially classed as a fragrance allergen that must be named on the label above threshold. The safety concerns that led to strict food limits relate to sustained ingestion, not to skin exposure at fragrance concentrations. As with any fragrance allergen, a small proportion of people can become sensitised.

EU law requires coumarin to be listed by name because it is one of the recognised fragrance allergens under Annex III of the Cosmetics Regulation. This labelling is mandatory when it exceeds 0.001% in leave-on products or 0.01% in rinse-off products, so that people who react to it can spot it. Seeing it listed means the product contains a declared, regulated fragrance ingredient, not that it is unsafe.

Coumarin is a recognised fragrance contact allergen and is one of the substances included in "Fragrance Mix II," a standard dermatology patch-test panel used to diagnose fragrance allergy. In sensitised people it can cause allergic contact dermatitis, though it is a less frequent culprit than some other fragrance chemicals. Patch testing by a dermatologist is the authoritative way to confirm a personal allergy.

Both forms are used. Coumarin occurs naturally in plants such as tonka bean, cassia cinnamon and woodruff, and it is also manufactured synthetically for perfumery. Because it is plant-derived or synthesised rather than animal-derived, it is generally suitable for vegan products; natural origin, however, does not reduce its allergen status.