What Is Keratin? Benefits for Hair and the Truth About Hydrolyzed Keratin

The question "what does keratin do" has two separate answers: in your hair, keratin is the main protein that gives the strand its structure and durability; in care products, it is hydrolyzed keratin, a care ingredient whose small pieces can cling to the surface of the strand and, under laboratory conditions, penetrate into damaged hair. Cosmetic products cannot rebuild the structure the hair has lost. Their effects are limited to the strand and are often temporary. Keratin straightening in salons is a completely different chemical process.

What does keratin do? Its role in hair

Keratin is the main structural protein of hair, the outer layer of skin and nails. You can think of a hair strand as having three layers: on the outside the cuticle, arranged like roof tiles; in the middle the cortex, which forms the body of the strand; and in thick strands, the medulla at the innermost.

The strength of the strand lies largely in the cortex. Here, helical keratin chains form fine fibers; a sulfur-rich matrix surrounds these fibers, and sulfur bridges (disulfide bonds) bind the structure together. The bonds explain the strand's durability, and the helical structure explains its flexibility. On the very outside of the cuticle there is a fatty layer called 18-MEA, which makes the strand water-repellent.

There is one important detail to know: a hair strand that has emerged from the scalp is no longer living tissue. It has no blood flow and no repair mechanism. A broken bond does not come back on its own, so the word "repair" in hair care should always be read in quotation marks.

Why does keratin structure break down?

• Heat: High heat damages hair proteins. You can find this topic in detail in the heat protectant article.
• Chemical treatment: Bleaching, permanent color and straightening reduce the bonds in keratin. In such treatments the cuticle opens, and friction and breakage increase.
• Sun and environment: Ultraviolet rays and environmental factors break down keratin over time, reducing the strength, flexibility and shine of hair.
• Alkaline products: They can remove the 18-MEA layer on the surface. Hair absorbs more water and tangles more easily.
• Friction: A rough towel, forcibly combing wet hair and tight tying mechanically wear down the strand.

The signs you can see are tangling, breakage, dullness and split ends. A single product cannot answer this entire list. The real precaution is to reduce the factors above.

What is hydrolyzed keratin?

Natural keratin is a large, water-insoluble structure. To be added to a shampoo or mask, it is broken into pieces; the Hydrolyzed Keratin you see on the label refers to these pieces. Its source is usually animal materials such as feathers, horn, hoof, hair or wool. The size of the pieces matters and is measured in Daltons:

• Small molecules below about 1.000 Daltons can enter damaged hair.
• Polypeptides below 10.000 Daltons are also reported to be able to spread into the strand.
• Larger pieces mostly stay on the surface and form a thin film.

The problem is this: the label does not state the molecule size. So from the word "keratin" you cannot tell whether these pieces enter the strand. It is also reported that damaged, especially bleached, hair holds more protein, so the result varies by hair. Instead of keratin, amino acid mixtures derived from plant proteins such as wheat, corn and soy are also used, but this does not mean these products will repair damaged structure. As one review states, keratin cannot be fully replaced by amino acids because of its mechanical properties.

What do the laboratory findings say, and how much of it carries over to the bathroom?

In a detailed study on this topic, very curly hair that had undergone chemical straightening was left for 24 hours in a solution containing hydrolyzed wool-derived keratin of three different sizes. The findings are interesting:

At first glance, impressive, right? But before carrying this result over to the bathroom, keep these in mind:

• The hair stayed in the solution for 24 hours. A shampoo contacts hair for a few minutes, a mask for 5-10 minutes.
• The study was done with hair from a single source and a single straightener, so the results cannot be directly generalized to other hair.
• The raw material manufacturer funded the study.
• Treated hair did not reach the breaking strength of never-chemically-treated hair at high humidity.
• The smallest molecule did not reduce breakage. The generalization "the smaller, the better" is also wrong.

So the laboratory finding is real, but it does not mean "the keratin in your shampoo repairs your hair." Independent studies with products used at home and real contact times are needed.

Why is the effect of keratin care temporary?

A dermatology review describes the situation clearly: protein-containing care products can temporarily smooth split ends, but excess protein clinging to the hair is removed when washed with shampoo. So the product must be reapplied for the effect to continue. It is also reported that current care products cannot permanently seal split ends.

This does not mean keratin products do not work. It is only necessary to name correctly what they do: this is surface care and, under certain conditions, limited support to the outer and middle layers of the strand. It does not erase the strand's history, and when you stop using it, hair gradually returns to its previous state.

Keratin in shampoo, mask and serum: the difference is in contact time

The same substance stays on hair for very different durations in different products. The table below compares usage, not effect.

The amount of keratin in products is not stated as a percentage on the label, and the order on the list does not give precise information about small amounts. So you cannot get an answer from the label to the question "which product has more keratin?" What you can do is use the product for the right purpose: shampoo is for cleansing, a mask is a rinse-off care step, a serum is a product that stays in the hair. For correct mask use, see the how to use a hair mask article.

Is a keratin product the same as keratin treatment?

No. The keratin product you use in the shower is a care product. Keratin straightening applied in a salon is a chemical process. What straightens the hair is not the keratin in the solution but aldehyde-type substances that cross-link with keratin, together with high heat. The straightening agent may be applied to the same spot 15-20 times in this process, and a dermatology review describes this as "very aggressive."

Formaldehyde is the most controversial part of these processes. The gas released with heat can cause watery eyes, coughing and throat burning. Moreover, it is reported that in products labeled "formaldehyde-free," measured values can exceed occupational limits. These treatments are not recommended in pregnancy; consult your doctor about this. So do not confuse the two uses of the word "keratin": one promises you a gentle care product, the other is a strong chemical process.

Do keratin supplements work?

Evidence for oral keratin products is limited. One study in this area ran over 90 days with 50 women; since keratin was given together with vitamins and minerals, it is not possible to attribute the effect to keratin alone. Studies in this area are usually small, short and linked to the company selling the product. There is no large, independent study showing that it stops hair loss.

If you are experiencing hair loss, it is more sensible to investigate the cause before trying a supplement. In cases of pregnancy, breastfeeding, chronic illness or regular medication use, make the supplement decision together with your doctor.

What can you do to protect the keratin in your hair?

Because lost structure is difficult to restore, the real gain is slowing the loss. The reasoning behind most of these steps comes from the damage list above:

• Leave space between chemical treatments. Leaving 8-10 weeks or longer between coloring, perming and straightening is recommended, especially in winter. Have one treatment done at a time. If two treatments are needed, first the perm or straightening, then the color two weeks later.
• Do not rub hair while washing. In a laboratory study, friction increased protein loss into the cleansing solution to about seven times that in water.
• Cover your hair in the sun. If you are outside for a long time, a wide-brimmed hat is a simple precaution.
• Tie hair loosely. Use a coated elastic; avoid tight buns and ponytails.
• Trim ends regularly. Cutting split ends to prevent their progression reduces breakage and shortening.
• Do not rub with a towel. Blot to absorb the water; do not force wet hair.

What should you expect from a keratin product, and what should you not?

Hair growth begins in the follicles beneath the scalp, while cosmetic products deal with the hair that has already emerged. Keep this distinction in mind when judging a product's contribution to appearance. Situations suggesting a health problem are different: widespread thinning, rapid heavy shedding, or a wound or itching on the scalp should prompt a visit to a dermatologist.