E920 — L-cysteine
E920 (L-cysteine), a flour treatment, is rated "safe": no significant concern. A natural amino acid used as a flour conditioner in commercial bread and pizza dough. Speeds gluten development. Sometimes derived from duck feathers or human hair.
What is L-cysteine?
A natural amino acid used to weaken gluten just enough to make commercial dough easier to mix and shape. Found in most supermarket sandwich bread, pizza dough, and bagels. Most modern production is from fermented bacteria, but some still comes from duck feathers or (historically) human hair.
What does it do to the body?
An amino acid your body uses normally. Safe at food levels. Vegans and some religious diets may want to check the source, which is rarely disclosed.
What regulators say
EFSA and the FDA both treat it as a safe additive with no numerical acceptable daily intake.
Risk rating: Safe
Cleared by EFSA with no significant concern at typical dietary exposure. Common, well-studied, and not a reason to put a product back on the shelf.