L-Cysteine

If you have heard one alarming thing about bread ingredients, it was probably this one. The claim is that the dough conditioner in supermarket bread and burger buns is made from human hair.

It is one of the few label rumours that is not simply false, and it is also not the whole story. Both halves of that deserve saying plainly.

What the regulation covers

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

That is the entire scope. A chemical identity, a use, and a limit.

What the regulation does not do is say what the L-cysteine was made from. There is no source requirement, and no line for one.

Where it actually comes from

L-Cysteine is an amino acid, abundant in keratin. Keratin is what hair, feathers, hooves and horns are made of, and hydrolysing keratin is the traditional industrial route.

Poultry feathers are the usual feedstock, being a byproduct of an industry that produces them in enormous quantity. Human hair has been used, principally by producers sourcing it where it is collected in volume. Bacterial fermentation is now an established route as well, and it produces material that is chemically identical.

So: an animal origin is real and common, a human origin is real and less common, and a microbial origin is real and increasing. The finished amino acid is the same molecule from all three.

Which is why the label cannot help

The ingredient list says L-cysteine, or sometimes just E920, and stops.

That places it exactly where Stearic acid and Mono- and diglycerides sit: a defined substance whose origin the label is not obliged to carry and therefore does not.

For halal and kosher observance the question is sharper than the vegan one, because a keratin source raises specific issues that certification bodies address directly and an ingredient list never will. The page on halal and kosher labelling is about exactly this class of problem, and this is one of the ingredients certification exists for.

Keeping the rumour in proportion

The permitted level is 0.009 part per 100 parts flour. That is a very small amount doing a very specific job: breaking some of the gluten bonds so that dough relaxes and machines can handle it quickly.

Whether that origin matters to you is a question about your own commitments rather than about risk, and this page is not going to tell you it should or should not. What we can say is that the rumour points at something real, the regulation is silent where people assume it speaks, and the answer lives in the supply chain rather than on the packet.