Is L-cysteine made from human hair?

Most viral claims about food ingredients fall apart on contact with the regulation. This one does not, and pretending otherwise would cost more trust than it saved.

What is true

L-Cysteine is an amino acid. It is abundant in keratin, the protein that makes up hair, feathers, hooves and horn, and hydrolysing keratin is the traditional industrial route to it.

Poultry feathers are the most common feedstock, being a byproduct of an industry that generates them in vast quantity.

Human hair has genuinely been used, principally by producers in regions where hair is collected in volume.

Bacterial fermentation is an established modern route producing chemically identical material.

All three are real. The finished amino acid is the same molecule whichever one it came from.

What the regulation says, and does not

The US regulation defines L-cysteine by its chemical name and formula, and permits it to supply up to 0.009 part per 100 parts of flour as a dough strengthener in yeast-leavened baked goods.

That is all. There is no source requirement and no place on a label for one.

So the ingredient list reads L-cysteine, or E920, and the question stays open. It is the same wall the page for people avoiding animal ingredients runs into again and again: a substance defined chemically loses its origin on the way to the packet.

For halal and kosher observance

Here the question is sharper, because a keratin source raises issues that certification bodies address explicitly and that an ingredient list is structurally incapable of answering.

This is one of the ingredients certification exists for. The page on halal and kosher labelling explains why the mark on the front of the pack outranks the list on the back in exactly this class of case.

Keeping it in proportion

The permitted level is very small, and the job is narrow: breaking some gluten bonds so dough relaxes enough to be machined quickly. It is not a preservative, a flavour or a nutrient.

Whether the origin matters to you is a question about your commitments rather than about risk, and this page takes no view on that. What we will say is that the rumour points at something real, the regulation is silent exactly where people assume it speaks, and the answer lives in the supply chain.