# Prenylthiol

> Prenylthiol (3-methyl-2-butene-1-thiol) is the volatile sulfur compound identified as the main source of cannabis's skunky aroma, potent at trace concentrations.

- Canonical: https://genetixbay.com/knowledge/glossary/prenylthiol.html
- Also written: 3-methyl-2-butene-1-thiol, 3MBT, 321MBT, 3-MBT, prenyl mercaptan, skunk thiol
- Glossary category: Cannabinoids and terpenes · Evidence: Supported
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Prenylthiol, chemically 3-methyl-2-butene-1-thiol (often abbreviated 321MBT), is a small prenylated thiol. Oswald et al. (2021, *ACS Omega*) identified it as the key compound behind the classic [skunk](https://genetixbay.com/knowledge/glossary/skunk.md) smell of cannabis, ending the long assumption that the smell came from [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md). It is the same compound responsible for "lightstruck" or skunky beer.

## In practice

Concentrations are tiny, too low for a standard [terpene panel](https://genetixbay.com/knowledge/glossary/terpene-test.md) to see, yet enough to dominate aroma because the human nose detects [thiols](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md) at extremely low levels. Detecting it takes specialised sulfur-selective [gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md), so it doesn't appear on routine COAs. In the 2021 study, related prenylated [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds were found across many cultivars, at different levels. That supports the grower observation that "skunk" is a genetic trait, not a product of feeding or curing tricks.

## Don't confuse with

- **Skunk (the animal)**: its spray uses different thiols, though the smell overlaps.
- **Terpenes**: present at much higher amounts, but not the skunk source.
- **Skunk (cultivar name)**: a lineage name, not a chemical measurement.

## Related terms

[Volatile sulfur compounds](https://genetixbay.com/knowledge/glossary/volatile-sulfur-compounds.md), [Terpene](https://genetixbay.com/knowledge/glossary/terpene.md), [Terpene profile](https://genetixbay.com/knowledge/glossary/terpene-profile.md), [Gas chromatography](https://genetixbay.com/knowledge/glossary/gas-chromatography.md)

## Read more

- [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md)

## Sources

1. Oswald IWH, Ojeda MA, Pobanz RJ, et al. 2021. Identification of a new family of prenylated volatile sulfur compounds in cannabis revealed by comprehensive two-dimensional gas chromatography. ACS Omega 6(47):31667-31676. https://doi.org/10.1021/acsomega.1c04196