Keratin

Proteins as the building blocks of hair and nails: three diverging paths behind one name

When hair becomes thin and nails split easily, will taking or applying keratin make them strong again? In short, while keratin is indeed a family of proteins that make up the skin, hair, and nails, it is important to first distinguish that oral supplements, topical applications, and high-heat salon treatments are not the same product. A single name is an ingredient that blurs different expectations.

Keratin is a building block for hair and nails, an ingredient in capsules, and the name of a salon procedure. Because the same word refers simultaneously to structural proteins in the body, oral supplements, surface coating treatments, and chemical smoothing procedures, it is easy to get confused about which form to choose. It is essential to distinguish these gaps.

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Keratin is not a single nutrient

Keratin is a family of proteins that form the intermediate filaments of epithelial cells. Different types of keratin exist in the skin, hair, and nails, and alpha-keratin is a fibrous protein abundant in these tissues. It is a group where various keratin genes and proteins work together, not a substance that can be defined as a single ingredient.

Therefore, it is difficult to simply say that "hair becomes weak due to a lack of keratin." The body synthesizes keratin using the necessary amino acids, and hair or nails are structures created as a result of that process.

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Oral keratin undergoes the digestive process

It is difficult to assume that oral hydrolyzed keratin moves to the hair shaft as an intact protein. This is because typical proteins are broken down into small peptides and amino acids in the stomach and small intestine before being absorbed. In other words, just because keratin is in a capsule does not mean it directly replenishes the building blocks of the hair or nails.

This is the first gap between expectation and reality. While oral keratin can serve as a protein source, it is not a method of filling the hair or nails with "completed keratin."

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Research remains at the level of preliminary signals

In a 90-day trial of 50 women, a complex containing 500 mg of branded keratin along with vitamins and minerals reported improvements in some hair and nail indicators. However, the sample size was small, and it is difficult to isolate the effect of keratin alone. The possibility that other ingredients in the complex contributed to the improvement cannot be ruled out.

A paper published in 2026 reviewing 14 studies on commercial oral hair supplements involving 967 people reported preliminary signals in some indicators, but the total hair count was not significant. It concluded that more rigorous and independent research is required.

In other words, the evidence to date is not strong enough to conclude that "taking it increases the amount of hair."

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Topical products and hair follicle growth are different stories

Keratin in shampoos or treatments is intended to temporarily change the feel and appearance of the hair surface. While it can cover damaged hair surfaces to make them feel smooth, the growth of new hair from the follicle is a different outcome.

If surface coating and follicle growth are not distinguished, the feeling that "hair texture has improved" can be mistaken for the effect of "new hair growing." Both relate to hair, but the point of action and the expected results are different.

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Salon keratin smoothing is another matter entirely

So-called "keratin smoothing" performed at salons may be easily mistaken as "replenishing keratin" due to its name, but it is actually a hair-smoothing procedure that combines heat and chemical treatments. Importantly, some smoothing products may release formaldehyde when heated.

This is not a question of the efficacy or toxicity of oral hydrolyzed keratin. The formaldehyde risk in salon products is a matter of exposure to heated products. It is necessary to check for labels such as formaldehyde, formalin, or methylene glycol and to receive the procedure in a well-ventilated space. Exposure must be stopped if irritation of the eyes, nose, or throat, or coughing and wheezing occur.

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You must consider accompanying supplements and complex ingredients

When choosing oral products, you should check the source of the keratin and the overlapping amounts of complex vitamins and minerals. Depending on whether it is a single-ingredient keratin supplement or a complex hair nutrient supplement containing biotin, zinc, and vitamins, the expected outcomes and precautions will differ.

If you have allergies to the raw materials, it is correct to avoid them. Additionally, there is insufficient safety data regarding long-term oral use for pregnant women, breastfeeding women, and children. So, what should you look for? First, distinguish whether the product is oral hydrolyzed keratin, a topical product, or a high-heat smoothing procedure, and prioritize checking the animal-based source, the amount of keratin, and the accompanying ingredients.

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Other causes of hair loss or nail changes must be checked first

If you experience sudden circular or widespread hair loss, scalp scarring or inflammation, or nail discoloration and pain, a medical evaluation takes priority over supplements. Various causes, such as thyroid dysfunction, iron deficiency, or changes in medication, may be hidden behind these symptoms.

It is important to check if there are underlying causes before considering supplements. Rather than the statement that keratin is the building block of hair and nails, the priority is to distinguish whether current hair loss or nail changes are simple nutritional issues or signals of another medical condition.

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Keratin produced by the body is different from oral keratin

Keratin produced by the body versus oral hydrolysates; hair surface coating versus follicle growth; single-ingredient keratin versus complex hair nutrients; and keratin smoothing versus formaldehyde exposure. These four distinctions resolve most of the confusion surrounding the name "keratin."

This ingredient cannot be simply summarized as "good to eat" or "restores when applied." This is because each form has different points of action and different supporting evidence.

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Criteria to Check Today

Rather than the statement that keratin is the building block of hair, the realistic criteria for evaluating this ingredient are whether it is ingested, applied, or performed as a procedure; whether it is a single or complex agent; and first identifying the cause of hair loss or nail changes. As expectations grow based on the name alone, it is more important to distinguish the different paths that diverge behind that name.

References

1. NCBI Bookshelf: The shape and structure of proteins.
2. NCBI Bookshelf: Physiology, Proteins.
3. Keratin complex for hair and nails: randomized trial.
4. Commercial oral supplements for hair growth: systematic review.
5. FDA: Formaldehyde in hair smoothing products.

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This text explains the origin of the raw materials, the scope of research, and precautions before consumption. As this cannot replace individual diagnosis or treatment, please consult a medical professional if you are taking medication or if symptoms persist. If sudden and severe symptoms such as difficulty breathing or decreased consciousness occur after consumption, seek help from 119 or the emergency room.