Sulfur-containing amino acid. HS-CH2-(Amino Acid Group). Most common residue involved in the formation of disulfide bonds when oxidized (only occurs on the exterior of cells, as the cellular environment is a reducing one). Common in hair, structural proteins and secreted amino acids.

Formula: C3H7NO2S
Molecular Weight: 121.16
Three-letter code: Cys
One-letter code: C
A sulfur-containing amino acid. Its sulfhydril group is very effective at binding free radicals and prevent their toxic effects. It is not one of the essential amino acids, but blood levels can easily be raised above baseline by supplementation. Cysteine's antioxidant function is similar to that of glutathinone, but cysteine is less expensive and more bioavailable.

Cysteins is particularly effective at preventing the cross-linking damage done by ethanol's toxic metabolite, acetaldehyde. Many sources recommend taking up to several grams of cysteine while drinking to prevent hangover (my personal experience supports the idea).

The biologically active isomer of cysteine is L-cysteine. It is often sold in the form of N-acetyl-cysteine, or NAC, which is a more stable molecule.
Information is from an article by Dr. Steven Fowkes at, though I've confirmed much of it elsewhere.

Cysteine has the following structure:


The sulfhydryl group has a pKa of 8.37.

None of the L-Cysteine nodes seem to tell you the most important thing!

Cysteine, or its derivative L-Cysteine, is commonly used in baking; pizza crusts, crisps/potato chips, donuts, Bagels, Croissants, Pita Bread, Crackers, Melba Toast and baby milk formula.

Where do they get cysteine? Human Hair! They grind down human hair, extract it and stick it in your food!

I will say it again because you need to know this... POTATO CHIPS, PIZZA AND BAGELS ARE MADE FROM HUMAN HAIR!

The human hair variety of cysteine is cheap and so is the most common. They get a lot of it from India where tonnes of hair is cut in religious rituals and they also get it from Japanese, Chinese and German heads...


It's not kosher either...

You can also get it from chicken feathers and cow horns. It can be produced artificially. But the majority of Cysteine used in USA is from human hair.

Enjoy your meal!

Log in or register to write something here or to contact authors.