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Other name(s):

a-amino-b-thiolpropionic acid

General description

Cysteine is a non-essential amino acid important for making protein, and for other metabolic functions. It's found in beta-keratin. This is the main protein in nails, skin, and hair. Cysteine is important for making collagen. It affects skin elasticity and texture. Cysteine has antioxidant properties.

Unsubstantiated claims

There may be benefits that have not yet been proven through research.

A form of cysteine called L-cysteine may help treat arthritis and hardening of the arteries. It may help treat certain lung diseases. These include bronchitis, emphysema, and tuberculosis.

Cysteine may play a role in the normal growth rate of hair. Cysteine may also help reduce the effects of aging on the skin. It may help healing after surgery or burns and protect the skin from radiation injury.

Cysteine may help burn fat and increase muscle mass.

Recommended intake

Amino acids (AAs) are available as single AAs or in AA combinations. They also come as part of multivitamins, proteins, and food supplements. The forms include tablets, fluids, and powders.

By eating enough protein in your diet, you get all of the amino acids you need.

There are no conditions that increase how much cysteine you need.

Side effects, toxicity, and interactions

Using a single amino acid supplement may lead to negative nitrogen balance. This can lessen how well your metabolism works. It can make your kidneys work harder. In children, single amino acid supplements may cause growth problems.

Don't take high doses of single amino acids for long periods of time.

Don't use cysteine supplements if you are pregnant or breastfeeding.

Don't use cysteine if you have either of these:

  • Diabetes. Cysteine may interfere with how insulin works.

  • Cystinuria. This is a rare genetic condition. It causes cystine build up. Cystine is related to cysteine. This buildup may lead to kidney stones that can block the urinary tract.

Online Medical Reviewer: Brittany Poulson MDA RDN CD CDE
Online Medical Reviewer: Tara Novick BSN MSN
Date Last Reviewed: 8/1/2023