Hair is mainly composed of a protein called keratin. Keratin is primarily made up of amino acids, particularly cysteine, which contributes to hair structure through disulfide bonds. In addition to keratin, hair also contains water, lipids, pigments (such as melanin, responsible for color), minerals and traces of other substances such as vitamins and sugars.

Here is a rough breakdown of the chemical composition of hair:

1. Keratin: Makes up approximately 65-95% of the dry weight of the hair. It is a fibrous protein that provides structure and strength.
2. Water: Makes up approximately 10-15% of the weight of the hair.
3. Lipids: These are natural oils produced by the sebaceous glands present in the scalp. Lipids provide lubrication and protection to hair.
4. Pigments: Melanin is the main pigment responsible for hair color. There are two main types of melanin: eumelanin (which gives dark shades) and pheomelanin (which gives light shades).
5. Minerals: Hair contains trace amounts of minerals such as calcium, iron, magnesium and zinc, which are important for hair health and growth.
6. Vitamins and other substances: Hair may contain traces of vitamins such as vitamin D and vitamin E, as well as other compounds such as sugars.

The exact composition of hair may vary slightly from person to person and can be influenced by factors such as age, gender, ethnicity and overall health.

Keratin is primarily composed of a series of amino acids that bind together to form a strong protein structure. Here are some of the most common amino acids found in hair keratin and their approximate percentages:

1. Cysteine: It is the most abundant amino acid in hair keratin and is particularly important because it forms disulfide bonds within the protein, giving it strength and structure. Cysteine makes up approximately 10-16% of the composition of hair keratin.
2. Alanine: It is another important amino acid present in hair keratin, which makes up approximately 7-12% of the composition.
3. Glutamine and glutamic acid: These amino acids are essential for the formation of keratin and make up approximately 5-8% of the composition.
4. Glycine: Contributes to the flexibility of keratin and makes up approximately 4-8% of the composition.
5. Proline: It is involved in the structure of the side chains of keratin and makes up approximately 4-6% of the composition.
6. Serine and tyrosine: These amino acids are present in smaller quantities, constituting approximately 2-4% and 1-3% of the composition of hair keratin respectively.

These percentages are approximate and may vary slightly based on several factors such as age, ethnicity and overall health. However, cysteine remains the most abundant and crucial amino acid for hair structure and strength.

• Knowing your hair | Introduction
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• Knowing your hair | The effluvium and the outflow
• Knowing your hair | What is hair made of?
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• Knowing your hair | Hydration guide
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