Healthy hair starts from the inside: What is keratin and what role does it play in maintaining healthy hair?

29 August 2023

Keratin, the major protein in hair strands is responsible for the strength and elasticity of the hair. So what makes our hair healthy and why is our hair sometimes lifeless?

There could be many answers.  But the most straightforward reason our hair looks tired and is full of split ends is that we have probably ignored the foundations of healthy hair.

The secret to healthy hair boils down to simple things: diet, sleep, hair care routine and genetics. While we can do little to change what we have inherited from our parents, we can take charge of what you do daily.

This article explains how you can transform your hair from lifeless to lustrous by taking care of it from the outside and inside.

A quick overview of hair structure

The human scalp contains about 1,500,000 hair strands. (1)

Each strand consists of two parts:

  • Hair shaft, which is visible and extends out of the skin
  • Hair root, which is in the skin and extends down to deeper layers in the skin

Each hair fibre has three layers:

  • Cuticle, the outermost moisture-repellent layer
  • Cortex, the middle layer made of protein (keratin), amino acids, minerals
  • Medulla*, the innermost layer made of proteins and fats

*The medulla layer may be absent in those with thin hair.

What is hair made of?

The building blocks of the hair shaft are proteins called keratins. The hair shaft contains 17 different kinds of keratins, which constitute up to 95% of the hair structure. (2,3)

Keratin is also found in your skin, nails, internal organs and glands. Unlike skin keratin, hair keratin is hard.

Amino acids in human hair keratin include: (4)

  • Alanine
  • Arginine
  • Aspartic acid
  • Cysteine
  • Glutamic acid
  • Glycine
  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Proline
  • Serine
  • Threonine
  • Tyrosine
  • Valine

3 Essential functions of hair keratin

The outer layer or cuticle is responsible for how your hair looks, feels and sustains.  The inner two layers—cortex and medulla—give your hair its colour and determine hair growth. Note that keratin is a crucial component of both the cuticle and cortex.

The critical functions of keratin in hair health are as follows: (5, 6)

  1. It protects your hair against damage caused by chemicals and environmental factors, such as heat, UV rays, and pollution.
  2. It makes your hair fibre resistant to breakage and improves elasticity.
  3. It helps balance moisture in your hair. 

Externally administered keratin, also called a keratin treatment, can help make your hair strong, less frizzy and appear shiny.

Likewise, it can make your hair straight if it is curly or wavy.

Though externally administered keratin does not prevent or treat grey hair, it can make your hair look smooth and healthy.

How fast does your hair grow?

According to The Trichological Society, hair usually grows between 0.5 and 1.7cm per month. (7) However, how fast hair grows varies widely, depending on genetics, general health, age, nutrition and pregnancy.

What causes different hair colours?

Hair colour depends on the amount of melanin and the relative amounts of eumelanin or pheomelanin in the cortex.

Melanin, made by cells called melanocytes, is a pigment that gives colour to your skin, hair, and eyes. Two types of melanin, eumelanin and pheomelanin determine hair colour. (8)

Eumelanin is dark while pheomelanin is light. Together, they result in a wide range of hair colours.

The following table shows how your hair colour forms.

Hair colorType and amount of melanin
BlackLarge amount of eumelanin
BrownModerate amount of eumelanin
BlondVery little eumelanin
RedMostly pheomelanin with a little eumelanin

Source: MedlinePlus. Is hair color determined by genetics?

What are the types of hair?

Conventionally, hair is classified into three types: African, Asian, and Caucasian/brown hair. (9)

African hair is drier, less dense and grows slower than Caucasian hair does. Moreover, it has more knots and breakages than other hair types. (10)

Asian hair is typically straight, dark, and thick. Among the three hair types, Asian hair is the strongest and has more compact cuticles. (11)

Caucasian hair is typically straight or wavy and is the thinnest. (12)

What happens as we get older?

As we age, we will likely notice your hair looks duller, thinner and grey.  Some people may lose a substantial number of hairs or even become bald.

Dry and dull hair may happen as the body produces less natural oils called sebum.

Age-related thinning often results due to two factors. First, ageing causes the hair diameter to narrow. Second, the anagen phase (period of hair growth when the hair fibre is continuously formed) shortens with increasing age.

Hair loss or baldness is mostly determined by your genes. However, it can also be associated with factors such as hormone levels, stress and illness.

Greying usually starts in the 30’s. It occurs when melanocytes make less melanin, causing your hair to appear grey or white. The age at which greying starts can vary with race. For example, Caucasians usually notice grey hair being mid-30s, that for Asians being late 30s, and that for Africans being mid-40s.

UK researchers in a 2009 study report that age-related hair colour changes could occur due to the accumulation of hydrogen peroxide produced by the hair follicles. (13)

Ageing, collagen, and hair loss: Is there a link?

Our body produces less collagen as we age. Studies show that collagen production declines by 1 per cent each year after the age of 20. (14) This decline certainly takes a toll on your skin, making it look rough, tired and wrinkly.

Understandably, we might be wondering if the same applies to our hair. Researchers are yet to find a direct link between decreased collagen levels and hair health. However, several reasons exist to support such a link.

For example, scalp health is crucial to optimal hair growth and retention. (15,16)  An unhealthy scalp means unhealthy hair and vice-versa. Studies show that an age-related increase in oxidative stress in the scalp impairs cuticle formation, leading to more brittle and damage-prone hair.

How collagen supplementation may promote hair health

Given the similar amino acid content of collagen and keratin, it is safe to say that collagen supplementation can help make our hair strong and healthy. The two main amino acids that make up keratin—proline and glycine—are also found in collagen.

The body breaks down orally ingested collagen into amino acids, which may be used to make keratin.

Collagen peptides also have strong antioxidant properties, which can help reduce oxidative stress in the scalp and prevent hair damage. (17)

Does hydration level affect hair quality?

There is no compelling evidence to suggest so.  But it is possible that dehydration may lead to an itchy, dry scalp, which can affect hair health.  And repeated scratching can damage the hair.

Also, the water we use to wash your hair can negatively impact hair health. For instance, hard water can cause breakage, thinning, dry scalp, frizziness and dullness. (18)


There are variations in hair type, but the condition of hair generally becomes less vibrant as we get older due to declining collagen / keratin production.  Externally, avoiding a hair regime which dries the hair might be avoided, whilst externally applied keratin and products which help to moisturise the hair can be beneficial and support healthy hair.

Beauty starts from the inside.  Poor diet, stress, alcohol and smoking affect the quality of all of our cells, including skin, nails and hair. Whilst a a nutrient-rich diet with plenty of anti-oxidants can mean the hair grows stronger and potentially quicker. 

The amino acids which are used to make keratin are found in collagen and a good quality collagen supplement may provide further support better quality, healthier looking and more vibrant,especially as we get older.


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  2. Mohamed Nasir, Nurdiena et al. “Potential use of human hair shaft keratin peptide signatures to distinguish gender and ethnicity.” PeerJ vol. 8 e8248. 30 Jan. 2020, doi:10.7717/peerj.8248
  3. Piccolo, Marialuisa et al. “Induction of Hair Keratins Expression by an Annurca Apple-Based Nutraceutical Formulation in Human Follicular Cells.” Nutrients vol. 11,12 3041. 13 Dec. 2019, doi:10.3390/nu11123041
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  6. University of Maryland, Baltimore County Magazine. Why does your hair curl in the summer? A chemist explains the science behind hair structure.
  7. The Trichological Society. Nutrition and hair health.
  8. Library of Congress. Why does hair turn gray?
  9. Daniels, Gabriela et al. “How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification.” International journal of cosmetic science vol. 45,1 (2023): 50-61. doi:10.1111/ics.12819
  10. Loussouarn, G. “African hair growth parameters.” The British journal of dermatology vol. 145,2 (2001): 294-7. doi:10.1046/j.1365-2133.2001.04350.x
  11. Leerunyakul, Kanchana, and Poonkiat Suchonwanit. “Asian Hair: A Review of Structures, Properties, and Distinctive Disorders.” Clinical, cosmetic and investigational dermatology vol. 13 309-318. 24 Apr. 2020, doi:10.2147/CCID.S247390
  12. Takahashi, T. Unique Hair Properties that Emerge from Combinations of Multiple Races. Cosmetics 2019, 6, 36.
  13. Wood, J M et al. “Senile hair graying: H2O2-mediated oxidative stress affects human hair color by blunting methionine sulfoxide repair.” FASEB journal : official publication of the Federation of American Societies for Experimental Biology vol. 23,7 (2009): 2065-75. doi:10.1096/fj.08-125435
  14. Scientific American. Why does skin wrinkle with age? What is the best way to slow or prevent this process?
  15. Tosti, Antonella, and James R Schwartz. “Role of scalp health in achieving optimal hair growth and retention.” International journal of cosmetic science vol. 43 Suppl 1 (2021): S1-S8. doi:10.1111/ics.12708
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  17. Chen, Yu-Pei et al. “Antioxidant and anti-inflammatory capacities of collagen peptides from milkfish (Chanos chanos) scales.” Journal of food science and technology vol. 55,6 (2018): 2310-2317. doi:10.1007/s13197-018-3148-4
  18. Srinivasan, Gautham, and Srinivas Chakravarthy Rangachari. “Scanning electron microscopy of hair treated in hard water.” International journal of dermatology vol. 55,6 (2016): e344-6. doi:10.1111/ijd.13141