Depends on Source
How we decideL-cysteine depends on its source. Industrial bakers add this amino acid to relax gluten and cut mixing time in bread, rolls, pizza bases, and croissants, and the supply comes from human hair, duck and chicken feathers, or plant fermentation. Bread often lists it as E920, but the origin is almost never stated, so the name on the pack tells you nothing about the animal.
Which animal, and does it die
- Comes from
- duck or chicken feathers, pig bristle, or human hair
- Requires slaughter
- Yes
- From a mammalRelevant to alpha-gal syndrome
- Pig is a common sourceRelevant to halal and kosher diets
These flags describe sourcing. They are not an allergen assessment, and a vegan label is not a free-from claim. If you have an allergy, read the allergen declaration on the pack.
Not required on labels
L-Cysteine used as a direct ingredient must be listed as 'L-cysteine' or 'E920'. However, when used as a processing aid at levels that don't remain in the final product, it may not need to be declared. Most commercial bread does list it if used.
- Source
- An amino acid used as a dough conditioner and reducing agent in commercial bread production. Can be sourced from: (1) human or animal hair [not vegan], (2) duck or chicken feathers [not vegan], or (3) fermentation from plant sources [vegan]. Source is almost never declared.
- Used In
- Commercial bread, rolls, pizza bases, crackers, croissants, some pastries. It relaxes gluten and reduces mixing time in industrial bakeries. Also used in some meat flavoring compounds.
- How to Avoid
- Artisan bread and sourdough almost never use L-cysteine (gluten develops naturally through fermentation time). Look for breads with short, simple ingredient lists. If L-cysteine is listed, contact the manufacturer to ask about the source.
Editorial Notes
This is one of the most uncomfortable entries in the vegan database. Historically, L-cysteine was predominantly sourced from human hair collected from barbershops and salons in Asia. This is still practiced but declining. Feather-derived cysteine (from poultry processing) is now more common. Fermentation-derived cysteine is available and increasingly used by brands targeting vegan and kosher markets.
In depth
How L-Cysteine Is Produced
L-cysteine is a sulfur-containing amino acid. Industrially, it is obtained through two broadly different routes, and the route determines whether the finished additive is vegan.
The traditional route is acid hydrolysis of keratin, a protein rich in cysteine. Keratin-heavy raw materials include human hair and duck or chicken feathers recovered from poultry processing. The keratin is broken down, and the cysteine is isolated and purified. Human hair was historically the dominant feedstock, much of it collected in Asia; feather-derived material has become more common as supply chains shifted.
The newer route is microbial fermentation. Selected bacteria are grown on plant-derived sugars and mineral salts and engineered or cultivated to secrete cysteine, which is then purified. This process uses no animal or human inputs and yields a product suitable for vegan, vegetarian, and many religious-dietary markets. The two routes produce a chemically identical molecule, so the finished ingredient cannot readily be distinguished by testing.
Where It Turns Up and Why the Label Rarely Helps
L-cysteine functions as a reducing agent. It weakens the disulfide bonds in gluten, relaxing the dough so it stretches easily and mixes faster. High-speed industrial baking values that, because it shortens processing time and improves machine handling.
The additive is most associated with commercial bread, soft rolls, burger and hot dog buns, pizza bases, bagels, tortillas, crackers, and laminated pastries such as croissants. It also appears in some savory flavoring systems, where its reaction products contribute meaty or roasted notes.
When added as a direct ingredient, it must be listed as 'L-cysteine' or by its E number, E920. The difficulty for consumers is the source. The label almost never states whether the cysteine came from keratin or fermentation. Two loaves with identical ingredient statements may use additives from entirely different origins, so the printed panel alone cannot confirm vegan status.
Vegan Alternatives and Avoidance
The most reliable way to avoid animal- or human-derived cysteine is to choose breads that never use the additive. Traditional sourdough and slow-fermented artisan loaves develop dough strength and extensibility through time, natural enzymes, and wild fermentation, so they typically contain no added dough conditioner at all. Short, recognizable ingredient lists are a useful signal.
Where a reducing or conditioning effect is wanted, bakers have plant-based options. Deactivated (inactive) yeast preparations supply natural glutathione, which acts as a reducing agent similar in principle to cysteine. Enzyme-based conditioners and vital wheat gluten adjustments can also manage dough handling without keratin-derived inputs.
Fermentation-derived L-cysteine is itself a vegan alternative to the keratin form, and some manufacturers specify it. When cysteine is unavoidable and the source is unstated, contacting the producer is the only way to confirm origin, as products certified vegan will use non-animal cysteine.
Naming, Certification, and Regional Notes
In the European Union and many countries that follow Codex-style labeling, L-cysteine is identified by the additive number E920. In the United States, it appears under its chemical name, not an E number, but the substance is the same.
Source origin matters beyond veganism. Cysteine from human hair or from non-certified animal feathers raises concerns in kosher and halal frameworks as well. That is one reason fermentation-derived and plant-fed cysteine has gained traction: it can more readily satisfy multiple dietary and religious certifications at once. Products carrying a recognized vegan certification, and often kosher-pareve marks, indicate that a non-animal cysteine source has been verified through the supply chain.
Labeling rules generally require the additive to be named, not its origin. Certification and direct manufacturer confirmation remain the practical tools for verifying that a given product's cysteine is plant-based.
Frequently asked questions
Is L-cysteine vegan?
It depends on the source. L-cysteine can be made from human hair, animal feathers, or plant-based microbial fermentation, and only the fermentation-derived version is vegan. Because labels name the additive but almost never state its origin, cysteine should be treated as non-vegan unless the product is certified vegan or the manufacturer confirms a plant source.
Is L-cysteine really made from human hair?
Yes, it historically has been. Human hair is rich in the protein keratin, which is broken down to extract cysteine, and hair collected in Asia was long a dominant feedstock. This practice is declining as feather-derived and fermentation-derived cysteine become more common, but keratin from hair is still used.
Is L-cysteine in bread?
L-cysteine is common in commercial and industrial bread. Bakers use it as a dough conditioner in products like soft rolls, burger and hot dog buns, pizza bases, tortillas, and laminated pastries, to speed mixing and relax gluten. Traditional sourdough and slow-fermented artisan breads usually contain none.
What can I use instead of L-cysteine?
Slow-fermented sourdough or artisan bread avoids it entirely. Time and natural fermentation build dough strength without additives. Where a conditioning effect is needed, deactivated yeast (which supplies glutathione) and enzyme-based conditioners are plant-based options. Fermentation-derived L-cysteine is itself a vegan alternative to the keratin form.
Is E920 the same as L-cysteine?
Yes. E920 is the European additive number for L-cysteine used as a flour treatment and dough conditioner. In the United States it appears under its chemical name, not an E number, but it is the identical substance.
Is L-cysteine halal or kosher?
It depends on the source, for the same reasons it depends for vegans. Cysteine from human hair or non-certified animal feathers is questionable under both halal and kosher standards. Fermentation-derived cysteine can more readily meet those certifications. Look for products carrying the relevant certification to confirm an acceptable source.