What Is Keratin And How Does It Affect Hair?

Keratin is a structural protein in the hair fibre. A cosmetic product containing keratin is different from the keratin your follicles produce, and a smoothing service is not a treatment for the cause of hair loss.

Key takeaways

• Conditioning benefits depend on the complete formula and how it is used.
• Hair-fibre experiments do not establish that a shampoo, supplement or salon service regrows hair.
• Salon smoothing products have safety considerations beyond whether the label mentions keratin.

Keratin and the hair shaft

The hair shaft contains keratin proteins and associated proteins arranged into a strong fibre. Its cuticle and cortex contribute to how the strand handles friction, stretching and chemical exposure. The Hair Cosmetics review explains these structures and the different actions of shampoos, conditioners, dyes and straighteners.

Bleaching, chemical processing, repeated friction and excessive heat can affect the fibre. Breakage along a strand is different from shedding from the follicle. See our hair-shaft guide for related structural conditions; a cosmetic product cannot identify their cause.

What keratin products can and cannot establish

Hydrolyzed proteins can interact with the hair surface, and some smaller protein components may penetrate damaged fibres. The effect depends on the ingredient, molecular size, formulation and condition of the hair. A smoother appearance does not mean a damaged strand has returned to its original structure.

In a 2018 study by Tinoco and colleagues, researchers tested eight keratin-based formulations on virgin and overbleached Asian hair. They measured mechanical and thermal properties, with improvements for particular experimental formulations. This was not a trial showing that every retail keratin product treats hair loss or that an oral supplement reaches the follicle and restores growth.

Choose a shampoo for cleansing and a conditioner for handling and conditioning needs. Assess the finished product rather than treating one ingredient as proof of superiority. Claims of deep repair, permanent split-end sealing or guaranteed growth need evidence for that specific claim and formula.

Salon smoothing and formaldehyde

A service sold as a keratin treatment may be intended to straighten or smooth hair. It is not equivalent to using a rinse-out conditioner. The FDA explains that some smoothing products release formaldehyde when heated, exposing customers and workers.

Read the ingredient list and ask about formaldehyde, formalin and methylene glycol, the product’s Safety Data Sheet, application training and ventilation. Professional application is not a guarantee that exposure or irritation cannot occur. The FDA discourages home application of these smoothing products. Stop using a product that causes a reaction and discuss symptoms with a healthcare professional.

Everyday care and supplements

The American Academy of Dermatology’s damage-prevention guidance recommends gentle handling, conditioning and reducing damaging styling practices. Lower heat and less frequent hot-tool use can help limit further damage. Our heat-styling guide gives related context.

The topical and hair-fibre studies discussed here do not establish that eating particular foods or taking keratin capsules repairs existing strands or regrows hair. Do not use a cosmetic quiz to diagnose a nutrient deficiency or select a medical treatment. Persistent thinning, patchy loss or scalp symptoms warrant assessment rather than repeated product trials.

Frequently asked questions

Is keratin the same as a hair-growth treatment?

No. Keratin’s structural role does not establish that applying or swallowing it treats the cause of thinning.

Does a keratin label prove that a product is safe?

No. Check the full formula, directions and intended use. A salon smoothing product and an ordinary conditioner require different assessments.

When should I seek advice?

If changes to hair care do not help, or you are concerned about hair loss, consult a dermatologist or another appropriately qualified healthcare professional. A stylist can advise on styling but does not replace medical assessment.

Sources

• Dias MFRG. Hair Cosmetics: An Overview. International Journal of Trichology. 2015;7:2–15.
• Tinoco A, et al. Keratin-based particles for protection and restoration of hair properties. International Journal of Cosmetic Science. 2018;40:408–419.
• FDA: Formaldehyde in hair smoothing products.
• AAD: How to stop damaging your hair.

This article provides general education, not an individual diagnosis or treatment prescription.