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Woman who has supplemented with keratin

What is keratin? Why should you take it?

Keratin works silently and effectively to support key aspects of our appearance. But why exactly should you consider supplementing with it?

Natural keratin: the star protein in hair, skin and nails

Identified in the 19th century, keratin is a natural insoluble protein produced by specialised cells called keratinocytes. Rich in sulfur, it is composed of 18 amino acids, predominated by cysteine (1).

Keratin exists in two distinct forms within the animal kingdom: beta-keratin (primarily in reptiles and birds) and alpha-keratin (in mammals, including humans) (2). The vegetable alternative, phytokeratin is obtained by hydrolysing plant proteins, mainly those from wheat and almonds.

In the human body, keratin is concentrated in the integumentary system, which includes the hair, skin and nails, where it plays a protective and structural role (3). Long used in the cosmetics and beauty industry, it is a common ingredient in hair care products: strengthening shampoos, masks, serums, and Brazilian smoothing treatments (for eliminating frizz) (4-5)!

What is keratin’s role in the body?

Keratin and hair

A key component of hair, keratin actually accounts for almost 95% of the composition of hair fibres, where it is present in different layers of the hair shaft (except the central medulla, which serves no particular function).

In the cuticle, the hair’s outermost layer, keratin binds the scales together, keeping them smooth and flat. In so doing, it makes this protective sheath more impervious to external assaults and at the same time, boosts its natural shine. A lack of keratin usually results in dull-looking hair, split ends or porous, brittle hair (6-7).

It is also present in pigmented form in the cortex, the hair shaft’s middle, and thickest, layer. This consists of a network of keratin filaments which follows the line of the capillary shaft, maintaining the hair’s elasticity (8).

Important: synthesis of keratin by the hair bulb is not a renewing process. It takes place solely during the anagen phase of the hair cycle, which corresponds to the period of hair growth. If hair is mistreated (using a too-hot hairdryer, repeated blow-drying, wearing elastic bands or hair slides ...), it cannot self-repair (9).

Keratin and nails

Produced in the matrix unguis (the base of the nail hidden under the skin), keratin gives nails their shine, strength and smooth appearance (10).

Weak, brittle, split or ridged nails can be a sign of a lack of keratin, though there are many other potential contributory factors to nail fragility: exposure to corrosive chemicals, trauma, fungal infections, poor diet (11)…

Keratin and the skin

The skin’s first line of defense, the epidermis is composed primarily of keratinocytes. These migrate from the epidermis’ deepest basal layer to its outermost one, the stratum corneum, becoming increasingly keratinised as they do so (12).

At the end of their journey, they differentiate into corneocytes, hard, flattened and keratin-filled dead cells, which fit together to form a cornified envelope. Smooth and strong, this has remarkable biomechanical properties (which ensure the skin’s resistance to friction), keeps the skin hydrated and prevents invasion by pathogens. Its exceptional cohesion is made possible by specific adhesive junctions (called ‘tight junctions’ and ‘desmosomes’) that keratin works to strengthen (13).

At the end of the cycle, corneocytes also undergo a process of desquamation, which is essential for the elimination of dead cells and skin renewal (14).

We can therefore see how the skin’s appearance is intrinsically linked to the condition of the stratum corneum and even more so, its keratinisation. More specifically, an insufficiently dense cornified envelope increases the risk of irritation and over-sensitive skin (15).

Keratin in dietary supplements

If you’re keen to have radiant hair, shiny nails, and a glowing complexion, then alongside a varied, balanced diet, keratin supplements can provide a significant beauty boost:

  • of the various forms of solubilized keratin on the market, the patented compound Cynatine HNS® has demonstrated visible efficacy on the appearance of hair and nails in clinical trials, an indication of its ability to ‘plug the holes’ in hair fibres (it can be found in the synergistic formulation Hair & Nails Formula, combined with vitamin B8 and zinc which also support healthy skin and hair) (16);
  • certain keratin supplements ‘cover all bases’ by including all the the best beauty nutrients (the product Daily Beauty combines Cynatine HNS® with collagen peptides, hyaluronic acid, avocado oil, biotin and zinc, in a unique all-in-one formulation) (17-18);
  • keratin is also used in supplements that focus more specifically on supporting a healthy glow (the product Tan Aid is based on Melaline®, a patented keratin hydrolysate extracted from black sheep wool which is high in melanin, the ‘tanning pigment’) (19);
  • in addition to keratin, some plant extracts contain bioactive compounds which reinvigorate lifeless hair (the nutricosmetic gem KeranatTM derives its benefits from plants such as millet, sunflower, wheat and rosemary, naturally rich in ceramides and miliacin) (20-21).



  1. Miniaci MC, Irace C, Capuozzo A, Piccolo M, Di Pascale A, Russo A, Lippiello P, Lepre F, Russo G, Santamaria R. Cysteine Prevents the Reduction in Keratin Synthesis Induced by Iron Deficiency in Human Keratinocytes. J Cell Biochem. 2016 Feb;117(2):402-12. doi: 10.1002/jcb.25286. PMID: 26212225.
  2. Sun X, Zhang Z, Sun Y, Li J, Xu S, Yang G. Comparative genomics analyses of alpha-keratins reveal insights into evolutionary adaptation of marine mammals. Front Zool. 2017 Aug 2;14:41. doi: 10.1186/s12983-017-0225-x. PMID: 28785294; PMCID: PMC5540548.
  3. Bragulla HH, Homberger DG. Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia. J Anat. 2009 Apr;214(4):516-59. doi: 10.1111/j.1469-7580.2009.01066.x. PMID: 19422428; PMCID: PMC2736122.
  4. Gavazzoni Dias MF. Hair cosmetics: an overview. Int J Trichology. 2015 Jan-Mar;7(1):2-15. doi: 10.4103/0974-7753.153450. PMID: 25878443; PMCID: PMC4387693.
  5. Weathersby C, McMichael A. Brazilian keratin hair treatment: a review. J Cosmet Dermatol. 2013 Jun;12(2):144-8. doi: 10.1111/jocd.12030. PMID: 23725308.
  6. An SY, Kim HS, Kim SY, Van SY, Kim HJ, Lee JH, Han SW, Kwon IK, Lee CK, Do SH, Hwang YS. Keratin-mediated hair growth and its underlying biological mechanism. Commun Biol. 2022 Nov 19;5(1):1270. doi: 10.1038/s42003-022-04232-9. Erratum in: Commun Biol. 2022 Dec 22;5(1):1406. Erratum in: Commun Biol. 2022 Dec 22;5(1):1407. PMID: 36402892; PMCID: PMC9675858.
  7. Tinoco A, Gonçalves J, Silva C, Loureiro A, Gomes AC, Cavaco-Paulo A, Ribeiro A. Keratin-based particles for protection and restoration of hair properties. Int J Cosmet Sci. 2018 Aug;40(4):408-419. doi: 10.1111/ics.12483. Epub 2018 Aug 28. PMID: 30047992.
  8. Yang FC, Zhang Y, Rheinstädter MC. The structure of people's hair. 2014 Oct 14;2:e619. doi: 10.7717/peerj.619. PMID: 25332846; PMCID: PMC4201279.
  9. An SY, Kim HS, Kim SY, Van SY, Kim HJ, Lee JH, Han SW, Kwon IK, Lee CK, Do SH, Hwang YS. Keratin-mediated hair growth and its underlying biological mechanism. Commun Biol. 2022 Nov 19;5(1):1270. doi: 10.1038/s42003-022-04232-9. Erratum in: Commun Biol. 2022 Dec 22;5(1):1406. Erratum in: Commun Biol. 2022 Dec 22;5(1):1407. PMID: 36402892; PMCID: PMC9675858.
  10. org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Structure of the nails. 2018 Jun 28. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513133/
  11. Dimitris R, Ralph D. Management of simple brittle nails. Dermatol Ther. 2012 Nov-Dec;25(6):569-73. doi: 10.1111/j.1529-8019.2012.01518.x. PMID: 23210755.
  12. Fuchs E. Keratins and the skin. Annu Rev Cell Dev Biol. 1995;11:123-53. doi: 10.1146/annurev.cb.11.110195.001011. PMID: 8689554.
  13. Murphrey MB, Miao JH, Zito PM. Histology, Stratum Corneum. [Updated 2022 Nov 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513299/
  14. Pierard GE, Goffin V, Hermanns-Le T, Pierard-Franchimont C. Corneocyte desquamation. Int J Mol Med. 2000 Aug;6(2):217-21. doi: 10.3892/ijmm.6.2.217. PMID: 10891569.
  15. Duarte I, Silveira JEPS, Hafner MFS, Toyota R, Pedroso DMM. Sensitive skin: review of an ascending concept. An Bras Dermatol. 2017 Jul-Aug;92(4):521-525. doi: 10.1590/abd1806-4841.201756111. PMID: 28954102; PMCID: PMC5595600.
  16. Beer C, Wood S, Veghte RH. A clinical trial to investigate the effect of Cynatine HNS on hair and nail parameters. 2014;2014:641723. doi: 10.1155/2014/641723. Epub 2014 Oct 16. PMID: 25386609; PMCID: PMC4214097.
  17. Bolke L, Schlippe G, Gerß J, Voss W. A Collagen Supplement Improves Skin Hydration, Elasticity, Roughness, and Density: Results of a Randomized, Placebo-Controlled, Blind Study. 2019 Oct 17;11(10):2494. doi: 10.3390/nu11102494. PMID: 31627309; PMCID: PMC6835901.
  18. Werman MJ, Mokady S, Nimni ME, Neeman I. The effect of various avocado oils on skin collagen metabolism. Connect Tissue Res. 1991;26(1-2):1-10. doi: 10.3109/03008209109152159. PMID: 1676360.
  19. Brenner M, Hearing VJ. The protective role of melanin against UV damage in human skin. Photochem Photobiol. 2008 May-Jun;84(3):539-49. doi: 10.1111/j.1751-1097.2007.00226.x. PMID: 18435612; PMCID: PMC2671032.
  20. Oh JH, Jeong KH, Kim JE, Kang H. Synthesized Ceramide Induces Growth of Dermal Papilla Cells with Potential Contribution to Hair Growth. Ann Dermatol. 2019 Apr;31(2):164-174. doi: 10.5021/ad.2019.31.2.164. Epub 2019 Feb 28. PMID: 33911565; PMCID: PMC7992683.
  21. Keophiphath M, Courbière C, Manzato L, Lamour I, Gaillard E. "Miliacin encapsulated by polar lipids stimulates cell proliferation in hair bulb and improves telogen effluvium in women". J Cosmet Dermatol. 2020 Feb;19(2):485-493. doi: 10.1111/jocd.12998. Epub 2019 May 28. PMID: 31135099.



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