The amino acids that the body cannot produce, and need to be taken in through the diet, are called essential.  Cysteine and cystine are two of these amino acids.  Cystine simply contains two molecules of cysteine bonded together, which increases stability.  Cysteine plays an important role in the formation of keratin and collagen, and the detoxification processes in the liver.  Keratin gives strength to the fingernails, toenails, skin and hair.

Collagen gives elasticity to all connective tissue including the skin and cartilage, found in the joints.  Thus cysteine helps maintain a youthful physical appearance and activity level.  Cysteine contains sulfur and forms sulphur-containing amino acids, like glutathione, which is used by the liver to detoxify harmful chemicals including those found in cigarette smoke, alcohol, aspirin and acetaminophen.  It also protects the body from radiation like that from the sun, industry or medical testing.  Cysteine increases the fluidity of mucus making it beneficial for clearing and improving healing of the respiratory tract.  Natural health practitioners for liver detoxification, skin problems, radiation damage, caner treatment, metal toxicity, respiratory disease and rheumatoid arthritis recommend cysteine.

Cystine is a stable molecule that combines two molecules of cysteine.  The body converts them back and forth easily.  The more soluble form is L-cysteine, making it a more effective supplement.  It is commonly found in capsules.  N-acetyl cysteine (NAC) is an activated form of cysteine that is used for increasing levels of the antioxidant glutathione, protecting against age-related damage and preventing side effects from cancer therapy.  See the article on NAC for more information.  Take amino acid supplements at least 1/2 hour before or after a meal to maximize their absorption.  If you take an individual amino acid supplement for longer than one month, take it with an amino acid complex to prevent the deficiency of other amino acids.

Toxicity with doses over 1000 mg is possible however some chronic diseases require these doses to see a medicinal effect.

Diabetics need for insulin may increase with cysteine use.  Do not use cysteine if you have cystinuria, an inherited kidney disorder.