What is cystine?

Qu'est ce que la L-Cystine ?

L-cystine is an amino acid composed of the combination of two L-cysteine molecules. It has numerous benefits, particularly for skin, nails and hair health. It has a wide range of applications in nutraceuticals, pharmaceuticals and infant nutrition. BCF Life Sciences is the only European producer with 30 years’ experience in extracting L-cystine from keratin obtained from poultry feathers. Find out more about cystine in our article!


Cystine, composed of two cysteine molecules

L-cystine was identified in 1810 by William Hyde, a British physicist and chemist. However, it was not until 1899 that it was officially recognised as a component of proteins.

Cystine is an amino acid resulting from the association of two cysteines. Composed of a carboxyl function, an amine function and a sulphur atom, cysteine gives cystine the particularity of containing two sulphur atoms.

When cystine is formed, bonds are created between the sulphur atoms. These covalent bonds are called disulphide bridges. Through oxidation-reduction reactions, cystine can be reduced to cysteine. When the pH is low, the form that occurs is cysteine, whereas when the pH is higher, the sulphur atom and its hydrogen atom are oxidised to L-cystine. Within a protein or between several proteins, the formation and breaking of these bridges play a role in the structuring of the protein. L-cystine is the most chemically stable form.

Cystine, composed of two cysteine molecules

The sulphur content of cystine gives this molecule its specificity. Sulphur is an important element for the body because it plays a role in biological functions, such as the synthesis of keratin. But what are the roles of cystine and its benefits for the body?


The roles and benefits of cystine

The beauty of hair, nails and skin


Skin, hair and nails, also known as phanera, can be enhanced by skincare but also by diet.

Numerous environmental factors, such as pollution, exposure to ultraviolet rays and chemicals, and our nutrition, all have an impact on the health of our skin.

💡 Did you know?

On average, an adult has 100,000 hairs.
And we lose between 50 and 100 hairs a day [1].

Cystine, a component of keratin, the protein of the skin

A balanced nutrition and certain food supplements are sources of cystine. Cystine is involved in the structure of keratin. The keratin protein forms filaments whose fibres are held together by cystine’s disulphide bridges. Keratin, produced by keratinocytes, is present in hair, nails and skin. It can be classified into two categories. Soft keratin present in the horny layer of the epidermis, containing between 2 and 4% L-cystine and hard keratin, present in the nails and hair, containing between 14 and 18% L-cystine. [2]

Keratin, produced by keratinocytes, an essential component of the skin


The synthesis of glutathione, a powerful antioxidant

As a precursor of cysteine, cystine is involved in metabolic pathways involving the synthesis of the antioxidant glutathione. It neutralises chemical oxygen species, also known as ROS (Reactive Oxygen Species), such as free radicals, oxygen ions and peroxides, which can have negative effects on the body [3]. Glutathione therefore helps to combat oxidative stress in cells, and hence cell ageing. In this way, the cystine/cysteine oxidation-reduction pairing helps to boost the body’s antioxidant status.

Cysteine, essential for the formation of glutathione

Glutathione can also help protect the skin from sun exposure. When the skin is overexposed to the sun, the cells undergo oxidative stress. Glutathione then acts as an antioxidant.

ROS also have other negative effects on the body. Their production is accompanied by oxidative stress, which inhibits the production of collagen. Collagen is a major protein in the body [4], whose main functions are to keep the skin firm and the joints comfortable. Glutathione plays an antioxidant role in the face of this oxidative stress, helping to combat the damage it causes.

To take advantage of the benefits of cystine, find out which sources contain it below.


Sources and uses of cystine

Cystine is present in protein-rich foods. Proteins can come from animal sources such as eggs, meat or dairy products, or from plant sources. The highest concentrations of cystine are found in dried egg powder and sesame seeds at between 1000 and 2000 mg/100 g of product, and in sunflower seeds, offal, beans and white fish at between 500 and 1000 mg/100 g of product. [5]

BCF Life Sciences offers stakeholders in the nutraceuticals market a range of ingredients containing L-cystine: Kera-Diet®, Cysti-White®, Naticol®-CySkin® and various granulometries of cystine, with promises ranging from the vitality and growth of hair and nails to skin health.

Other uses for cystine are also taking place in many sectors, such as infant nutrition. Nevertheless, it is essential to study the recommendations and regulations before launching a cystine-based product.

To sum up, cystine has multiple benefits for the body, in particular for the beauty of the skin, nails and hair, by playing a role in the synthesis of glutathione, a powerful antioxidant.

What if you added cystine to the centre of your formulations?



  • [1] Blume-Peytavi, U. Tosti, Hair Growth and Disorders, 2008
  • [2] Mitsui and al, Adult T cell leukemia (ATL)-derived factor/human thioredoxin prevents apoptosis of lymphoid cells induced by L-cystine and glutathione depletion: possible involvement of thiol-mediated redox regulation in apoptosis caused by pro-oxidant state, 1997
  • [3] Med Sci (Paris). Reactive oxygen species and oxidative stress, 2011
  • [4] Anna Sorushanova and al. The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development, 2019
  • [5] Ajinomoto database, 2016