Hair fiber structure and keratin biology
The structure of the hair fiber
Key takeaway for patientsA strand is only as good as the follicle that made it. Changes in the quality of hair can reflect nutrition, hormones or general health.
A hair is made of keratin, a tough protein built in the follicle. The visible shaft has three layers: the cuticle, overlapping scales that protect the surface; the cortex, which gives the hair its strength and holds its pigment; and, in thicker hairs, a central medulla.
The shaft itself is not living tissue. Its quality is decided in the follicle, where rapidly dividing cells depend on a steady supply of protein, iron, zinc and other nutrients.
Key steps in building a hair
- Cell division in the hair matrix
- Cells at the base of the follicle divide rapidly.
- Keratin synthesis
- The cells fill with keratin proteins.
- Keratinization
- Disulphide bonds cross-link the keratin and harden the fiber.
- Emergence
- The finished shaft, coated in lipids from the sebaceous gland, leaves the scalp.
Factors that weaken the fiber
Some act on the follicle, others on the shaft after it has grown:
- Nutritional deficiency
- Low protein, iron or zinc limits what the follicle can build.
- Heat and chemical processing
- Lift the cuticle and break disulphide bonds.
- UV exposure and weathering
- Degrade proteins and pigment along the shaft.
- Thyroid and hormonal changes
- Alter the texture and diameter of new growth.
Clinical management and physician guidance
Assessment looks at the hair and scalp and at general health.
- Clinical and laboratory assessment
- Examination of hair and scalp, with ferritin, thyroid function and other tests where indicated.
- Physician-guided care
- Nutrition and any underlying condition are addressed as your physician decides.
- Monitoring and follow-up
- Hair grows slowly, so change is judged over months.
Research focus in hair biology
| Core focus area | Biological target | Clinical relevance |
|---|---|---|
| Fiber structure | Keratins and keratin-associated proteins | Strength and elasticity of the shaft |
| Surface integrity | The cuticle | Protection against weathering |
| Follicle metabolism | Proliferation of hair matrix cells | Nutrient needs of growing hair |
| Pigmentation | Follicular melanocytes | Hair color and graying |
Frequently asked questions
- Can damaged hair repair itself?
- No. The shaft is not living tissue; new, healthy growth comes from the follicle.
- Does diet affect hair?
- Yes. The follicle needs protein, iron and other nutrients to build hair.
- When should I see a physician?
- For sudden shedding, patchy loss, or changes that come with other symptoms.
Academic references and literature
- Schweizer J et al. (2007). Hair follicle-specific keratins and their diseases. Exp Cell Res, 313(10), 2010-20. PMID 17428470.
- Almohanna HM et al. (2019). The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatol Ther (Heidelb), 9(1), 51-70. PMID 30547302.
This guide belongs to the Hair Growth program