What Is the Difference Between Cysteine and Cystine?

If cystine levels become extremely high cystinosis may occur, causing kidney stones.
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  • Written By: Jennifer Long
  • Edited By: Melissa Wiley
  • Last Modified Date: 23 February 2015
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Cysteine and cystine are two types of amino acids produced by the body, which means that they are classified as non-essential amino acids. Both of these two amino acids are necessary for certain, though differing, aspects of health. Cysteine helps promote skin protection through white blood cell and collagen production and assists in the production of an antioxidant known as gluthathione, while cystine can aid in surgery recovery, hair growth, and treatment of anemia. Cystine is produced in the body from two cysteine molecules. Despite this, cysteine and cystine work differently to maintain health.

Levels of cysteine and cystine can be increased through dietary supplements that can be used for various purposes. A specific protein called alpha-keratin contains a large amount of cystine and is responsible for hair and fingernail growth. Many over-the-counter aging reversal or preventative products contain alpha-keratin because of cystine and its potential benefits. Cysteine is believed to trigger the growth of collagen and increase the elasticity of the skin. Studies have shown that cystine can improve the health and growth of hair.


In addition to the influences that cysteine and cystine have on skin, collagen, and new hair growth, research has shown that cysteine has influences on other aspects of the body. Cysteine has the ability to aid in the body’s production of gluthathione, which is an antioxidant. This antioxidant may be able to help reduce the risks of developing some types of cancer and artery hardening. Many doctors believe that cysteine can help break up mucus that can be found in patients with bronchitis and emphysema.

Another difference between cysteine and cystine is in how the body absorbs the supplements. The body absorbs cysteine more easily than cystine, so supplements are more commonly made of cysteine. Additionally, cystinosis can be a complication that occurs when cystine levels in the body are extremely high. Cystinosis is a disease that leads to the development of crystals that cause kidney and bladder stones.

Although cysteine and cystine are produced naturally by the body, there are instances when cystine or cysteine supplements are ideal. Methionine is an amino acid that is responsible for the body’s creation of these other two amino acids. It is not a non-essential amino acid and therefore is not produced naturally by the body. If a person does not obtain adequate amounts of methionine through food, cystine and cysteine levels are affected. Supplements of these two amino acids can help bring levels in the body back to normal, making them potentially beneficial.



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