Olfactive Chemistry: Indole- The Sour Inside

In the middle of the movie America Hustle one of the characters has this quote, “It’s like that perfume you love, that you can’t stop smelling even when there’s something sour in it.” Of course I have no idea exactly what she is referring to but in my mind while watching there was only one perfume ingredient which fit this description, indole.

Indole is the “bad girl” of perfumery. Cue Donna Summer. They are found naturally in the group of floral notes dubbed “white flowers”. Jasmine is the leader of that family and in the specific species of jasmine called jasminum sambac you will find the highest amount of natural indole. It is why the synthetic jasmines exist, to remove the indole, to get a brighter fresher version of jasmine. I very often make the distinction in reviews with the essential oil being a little more experienced and the synthetic being a scrubbed-fresh debutante. Both have their place on the perfumer’s palette.

indole skatle

Indole gets a bad rep because of the methyl-substituted version of indole known as Skatole. As you can see above there is only the addition of one methyl group different between Indole and Skatole. Skatole is the smell of feces and it is what many associate with the word indole. Indole by itself in high concentration smells more like mothballs. What is particularly magical is what happens as you dilute indole down in alcohol solutions. When you have a 10% solution of indole in alcohol it smells like an old closet. Dilute it in half to 5% and you get that dirty skin smell. Dilute it again in half to 2.5% and now a subtle kind of decaying sweetness becomes evident. Take it to 1.25% and an almost floral-like quality comes out. Reduce it finally to 0.5% and you have a building block to work with.

Indole is easily synthesized in metric ton quantities and is one of the more cost-effective perfume materials to use. Once you get used to handling it in its different iterations depending on the concentration. It allows a perfumer on a budget to take synthetic jasmine and a bit of indole to create a simulation of jasminum sambac.

Good examples of indolic perfumes are naturally the jasmine-focused ones. Serge Lutens A La Nuit and Diptyque Olene really wear their indole on their sleeve. One which is composed of indoles and synthetics is the original Calvin Klein Eternity which not only sports a high concentration of indole but also Iso E Super, and Galaxolide. Eternity is one of the best-selling perfumes of all time. While the time period is not right it is the perfume I think best represents the quote I began this with.  

Mark Behnke