CYSTEINE (Cysteine) – function in cosmetics

A sulfur-containing amino acid used in hair products and as an antioxidant.

What it is

Cysteine is a sulfur-containing amino acid with a thiol (-SH) group; in its L form it is one of the building blocks of proteins, including hair keratin. CosIng lists it as an antioxidant, antistatic, hair-conditioning, hair-waving or straightening, fragrance and reducing ingredient.

Where it is used

Found in hair waving and straightening products, hair care products and some skin care products.

Limits of interpretation

The INCI list shows which ingredients are present, not how much of each. Above 1%, ingredients are listed in descending order of weight; below 1% the order is free.

The CAS numbers given cover both L-cysteine and the DL form; the label does not show which form is used.

Functions

Antioxidant

Inhibiting reactions promoted by oxygen, thus avoiding oxidation and rancidity.

Antistatic

Preventing and/or reducing static electricity by neutralising electrical charge on surfaces.

Hair conditioning

Enhancing the appearance and feel of hair. Leaving the hair easy to comb, supple, soft and shiny and/or imparting volume, lightness, gloss, texture, etc.

Hair waving or straightening

Modifying the chemical structure of the hair, allowing it to be set in the style required (permanent waves or hair straightening).

Fragrance

Imparting an odour or taste. Creating a perceivable pleasant smell and/or masking a bad smell.

Reducing

Changing the chemical nature of another ingredient by adding hydrogen (or removing oxygen).

CYSTEINE

What it is

Where it is used

Limits of interpretation

Functions

EU regulation

Products with this ingredient (12)