For centuries, one of the world's most prized perfume ingredients came from an unlikely source: the intestines of sperm whales.

Ambergris is a rare, waxy substance thought to form in the digestive tract of sperm whales. Sperm whales eat enormous numbers of squid, but they cannot digest the squid's hard, sharp beaks. Researchers believe that in the small percentage of whales that produce ambergris, the digestive system coats these irritating fragments in a fatty substance, creating a mass that may help protect the whale's intestinal tract from injury. 

Pieces were found floating at sea or washed onto beaches, sometimes after spending years exposed to salt water, sunlight and air.

Fresh ambergris is dark, soft and distinctly unpleasant-smelling. But time at sea transforms it. As it weathers and oxidizes, it becomes lighter and develops a complex scent described as musky, earthy, woody, sweet and marine. The chemistry changes as well: ambrein, a largely odorless compound in ambergris, breaks down through oxidation into highly aromatic molecules responsible for much of its characteristic fragrance.

People discovered its appeal through experience rather than chemistry. Ambergris was burned as incense, added to foods and medicines, and eventually became highly prized by perfumers. They found that tiny amounts could add depth to a fragrance while also acting as a fixative, helping other scents linger longer.

Its origin remained a mystery for centuries. Ambergris was variously thought to be sea foam, tree sap or fungus. 

The mystery began to clear as the sperm-whaling industry expanded and whalers found ambergris inside the whales themselves. By the late 18th century, scientific accounts had firmly linked the mysterious perfume ingredient to the sperm whale.

Today, perfumers can reproduce its most desirable effects with synthetic and semisynthetic compounds such as Ambrox, avoiding the need for natural ambergris.