Ambergris is perfumery's most legendary ingredient, a waxy substance produced in the digestive tract of sperm whales and aged for years by ocean currents until it develops a complex scent. Real ambergris smells salty, warm and animalic, like driftwood, tobacco and skin with a strange marine sweetness. Because natural ambergris is rare and expensive, most modern perfumes use ambroxan, its synthetic counterpart. It acts as a fixative, making fragrances last longer while adding a radiant, skin-like warmth. In Indian heat, ambergris-based drydowns are lovely because they sit close to the skin rather than projecting heavily. You will find its character in many modern blue and fresh fragrances where it creates that clean-yet-warm finish that lasts all day.