Coumarin is a potential allergen (and hepatotoxic in larger quantities) and hence has to be listed in the LOI if it’s present above a certain level (EU: 0.001 in leave-on and 0.01 in rise-off products). The origin of coumarin is usually the added perfume (in which coumarin may be present as part of an EO or because it has been added in pure form). The level therefore is commonly very low (EU regulates oral intake from food at 0.1 mg per kg body weight per day) but it’s present in many perfumes and transdermal assimilation might push daily uptake above the allowed amount.