Costus

Costus is the root of Saussurea costus, a tall thistle-like plant of the western Himalaya, and it is one of the very few aromatics that appears as a standard drug in Greek, Roman, Indian, Chinese and Arabic medicine at the same time. Dioscorides has it, the Ayurvedic texts have it as kuth or kushtha, Chinese medicine has it as mu xiang, and the Arabic materia medica has it as qust.

Its position in Islamic tradition is unusual for a plant. Several hadith recommend qust al-hindi, Indian costus, and describe it as among the best remedies available, which gives it a standing within prophetic medicine that ordinary aromatics do not have. It is still widely sold across the Muslim world on that basis, powdered, and used as a snuff, an oil and a burned incense.

In Indian practice it is an ingredient of compounded temple incense and a drug for skin conditions, which the Sanskrit name may reflect.

The plant is CITES Appendix I listed, which is the strictest category, following collapse of the wild Kashmiri populations. Cultivation in Himachal Pradesh and elsewhere now supplies the legal trade, and a good deal of what circulates in the herbal trade is another Saussurea species, or is not Saussurea at all.

Costus root oil has one of the more divisive profiles in perfumery. It is usually described as animalic: warm, dirty, and specifically like unwashed hair or wet dog, with a violet-like sweetness underneath. Used at trace levels it gives a skin-like depth that is difficult to obtain any other way, and it was a component of several classic twentieth century compositions.

It is now essentially banned. The International Fragrance Association restricted costus root oil after it was identified as a potent skin sensitiser, and the material was withdrawn from general perfumery use. Reformulations of older perfumes that relied on it are among the more audible casualties of the sensitiser restrictions, and substitutes have never quite matched it.

The restriction applies to the oil rather than to the root, which is why costus continues in medicinal and incense use in the traditions that use it while having largely disappeared from Western fine fragrance.

That split is worth noticing as a general pattern. Several traditional aromatics have been regulated out of one market on toxicological grounds while continuing without interruption in another, and the difference is usually the route of exposure: a burned resin, a snuffed powder and a skin-applied oil are three different risk profiles for one substance, and only the third is what the fragrance regulations are about.