Is Cysteine vegan?
Cysteine
L-Cysteine is a naturally occurring sulfur-containing amino acid that oxidises to form the disulfide cystine. It is used in cosmetics as a hair-conditioning agent and in food processing. It can be sourced from animal keratin (hair, feathers) or produced synthetically/by fermentation.
Why unconfirmed?
Cysteine can be either derived from animal, or non-animal sources. The ingredient name itself is identical either way, so the label alone can’t tell you which. Only a supplier declaration can.
| Also known as | 2-Amino-3-mercaptopropionic acid, Half-cystine, L-Cysteine, L-Cysteine hydrochloride |
|---|---|
| INCI name | Cysteine |
| E number | E920 |
| INS number | 920 |
| CAS number | 3374-22-9 |
| EC number | 200-158-2 |
| CosIng ID | 75422 |
| Last verified | 16 August 2026 |
An ingredient is considered vegan if it contains no animal-derived components at any point in its production.
Selling a product with this ingredient? A supplier declaration can confirm the source. See how certification works.
Classifications are made to the best of our knowledge based on available scientific and regulatory sources. We cannot guarantee the accuracy of every entry, errors in the sources we draw from can always occur. This tool also cannot account for cross-contamination, which depends entirely on individual suppliers and producers. If you believe a classification is incorrect, you can report an issue.
