One reason why oud is so expensive is its rarity. By some estimates, fewer than two percent of wild agar trees produce it.

"It is quite a rare occurrence naturally …. [Around] one in 10 trees usually show signs of agarwood production while the other plants in the same population may not necessarily have agarwood," says Joachim Gratzfeld, who works for Botanic Gardens Conservation International and for years has been trying to preserve the trees that produce oud.

He explains that there are no obvious external signs that a tree may contain agarwood and, even if it does, the quantity can only be fully determined after the tree has been felled. The result is indiscriminate logging of trees and a drastic decline in wild aquilaria species over the last few decades.

The science behind oud

Assam in India was originally home to one of the largest areas of wild and naturally occurring agarwood trees. But indiscriminate logging has changed all that, and now a country that was once one of the main suppliers of agarwood has banned its harvesting and has to import it.

The trees have been put on the list of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). In some countries this has led to a ban on harvesting, and in others to a requirement for a CITES certificate for export, proving that the wood came from a sustainable source.

Commercial plantations have also been established in many countries, and yet, in the wild, the tree’s population continues to decline.

But that has done nothing to slow down demand. Now, nearly all the major perfume brands have an oud-based collection.

Behind the growing popularity of oud

According to market research company NPD Group, sales of oud perfumes are increasing within the prestige fragrance market, which is valued at $3bn globally. A 2013 report showed that total oud sales were up by 68 percent.

The French perfume company Henry Jacques has been developing oud perfumes for around 30 years, long before it became fashionable in the West.

"Suddenly everybody discovered the beauty of this component," says Anne-Lise Cremona, a perfumer and daughter of the founder, Henry Jacques.

The smell of luxury: Inside the world of perfume

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