Are there any risks of using keratin products too often on fragile hair?

Keratin treatments and keratin-based products are often introduced as solutions for hair that appears weak, frizzy, or damaged. At first glance, the idea of reinforcing hair with the same protein it is naturally made of seems logical. Yet, when the subject is fragile hair—hair that already struggles with breakage and thinness—the question shifts from cosmetic improvement to the possibility of harm. What happens if we expose this type of hair to repeated doses of keratin and the procedures required to apply it?

Research suggests that the risk is real: the very process that promises to protect may, when overused, contribute to damage.

When reinforcement turns into rigidity

Keratin is a fibrous protein, and it is a natural component of human hair. In cosmetic products, keratin is applied externally to coat the hair shaft and create a smoother surface. But the idea that external keratin integrates seamlessly into fragile hair is misleading. A review published in 2014 in the Journal of Cosmetic Dermatology evaluated the impact of keratin-based treatments on hair fibers and reported that chemical processes used to attach keratin often alter the hair cuticle, the protective layer of the strand (Gavazzoni Dias, 2014). Altering the cuticle may create the impression of strength initially, but over time, especially in already fragile hair, the rigid structure can lose flexibility, making strands more likely to snap.

The hidden role of chemical agents

The discussion around keratin products cannot ignore the chemicals that make the treatment possible. Keratin on its own cannot bind permanently to hair; it requires chemical assistance. Many salon-based treatments rely on formaldehyde or ingredients that release formaldehyde under heat. In 2021, the U.S. Food and Drug Administration issued warnings about hair-smoothing products, stating that exposure to these substances can irritate the scalp, eyes, and lungs (FDA, 2021). Beyond health concerns, these chemicals affect the structure of the hair fiber by depleting natural moisture, which fragile hair needs to maintain elasticity. Without elasticity, hair is less able to bend under tension, and breakage becomes more likely.

Shine versus structure

The attraction of keratin lies in its immediate effect: shiny, smooth strands. But temporary gloss does not necessarily mean long-term health. A 2016 study published in the International Journal of Trichology examined the effect of heat treatments commonly paired with keratin procedures. Researchers measured the elasticity of treated hair and found that thermal exposure decreased the ability of strands to return to their original shape after stretching (Martins et al., 2016). For fragile hair, this loss of elasticity has a critical consequence. When strands are pulled during brushing or styling, they no longer rebound but break.

Research on repeated applications

In 2019, researchers investigated how repeated keratin applications affect human hair. The study, published in Clinical, Cosmetic and Investigational Dermatology, exposed hair samples from 20 women to keratin products and heat styling over an eight-week period. Results indicated that after one application, hair appeared stronger when measured for tensile strength, meaning it could resist more force before breaking. However, repeated applications led to a decline in this strength. The hair became rigid and developed microfractures, which are small but accumulating weaknesses in the fiber (da Silva et al., 2019). The method used—stretching treated hair until breakage—highlighted how fragile hair does not benefit from cumulative keratin exposure. Instead, the coating effect reaches a point where protection turns into vulnerability.

Limitations of the evidence

While these studies provide insight, they also come with limitations. Many experiments use hair samples detached from the scalp, meaning they lack the protective role of sebum, the natural oil produced by follicles. Most research also involves small participant groups, such as the 20 women in the 2019 study, which makes it difficult to generalize results to all hair types and ethnic backgrounds. Additionally, not all keratin products contain the same concentration or additives. Despite these variations, the consistent finding is that fragile hair faces specific risks when keratin treatments are repeated too often.

If we ask whether there are risks of using keratin products too often on fragile hair, the answer is yes. The process may give an impression of strength and smoothness at first, but repeated applications weaken the internal structure of already vulnerable strands. Exposure to heat and formaldehyde-based chemicals further accelerates dryness and breakage. **For someone with fragile hair, it is not a matter of whether risks exist, but how quickly those risks outweigh the temporary shine. **

Understanding that keratin is not a restorative cure but a cosmetic layer helps frame what is happening to the hair: short-term gloss at the expense of long-term stability.

References

da Silva, R. C., Barros, C. H., & Rodrigues, L. (2019). Effects of keratin treatments on tensile strength and morphology of human hair fibers. Clinical, Cosmetic and Investigational Dermatology, 12, 519–527. Retrieved from https://www.dovepress.com/effects-of-keratin-treatments-on-tensile-strength-and-morphology-of-hu-peer-reviewed-fulltext-article-CCID

Food and Drug Administration (FDA). (2021). Hair smoothing products that release formaldehyde and related chemicals. U.S. Food and Drug Administration. Retrieved from https://www.fda.gov/cosmetics/cosmetic-products/hair-smoothing-products-release-formaldehyde-and-related-chemicals

Gavazzoni Dias, M. F. R. (2014). Hair cosmetics: An overview. Journal of Cosmetic Dermatology, 13(2), 120–127. Retrieved from https://pubmed.ncbi.nlm.nih.gov/24836682/

Martins, M. A., de Carvalho, R. R., & de Almeida, H. L. (2016). Influence of thermal treatments on hair shaft morphology and elasticity. International Journal of Trichology, 8(1), 14–18. Retrieved from https://journals.lww.com/ijot/fulltext/2016/08010/influence_of_thermal_treatments_on_hair_shaft.4.aspx