The Science of Keratin: Your Guide to Strong, Healthy Hair

Last updated: January 2025 | Reading Time: 12 minutes | Written by: Sins 'n Lashes Expert Team

Have you ever wondered why some hair shines like silk while others just break? The answer often lies in a single, tiny building block: Keratin. If you understand how this protein works, you have the key to your dream mane in your hand.

In this guide, we'll skip the jargon (or just explain it!). We'll show you exactly what keratin is, why your hair is crying out for it and how you can use it to finally stop hair breakage.

What is keratin & Where does the hair protein come from?

Think of keratin like the bricks of a house: It's a super stable proteinthat makes up much of your hair, nails and the top layer of your skin. Keratin can come from various sources - not only from human hair, but also from animal sources, such as sheep's wool or alpaca wool. Incidentally, your hair consists to a very large extent of keratin (almost 80%).

Keratin is like a "protective and stabilizing substance" in the body. It is not only found in hair, nails and skin, but also in the claws, hooves, horns, beaks and feathers of animals. Keratin forms the top protective layer in your skin. This layer helps to protect the skin from friction and minor injuries, keeps harmful substances out and ensures that the skin does not dry out as quickly. In short: keratin provides structure, protects and keeps everything "in shape".

How healthy your hair, skin and nails look depends largely on how well this keratin structure is. When keratin is "well structured", hair often looks smoother, stronger and shinier - and nails break less quickly. This is why keratin plays a major role in hair care - for women, men, in fact for everyone who values a well-groomed appearance.

Without these "bricks", your hair would simply collapse. It would be rubbery, brittle and would not reflect any shine. But not all keratin is the same. Here's the difference:

Keratin chemistry: amino acids & Hair structure

Okay, quick trip to chemistry class (I promise, it'll stay simple!). Your keratin is made up of 18 different amino acids. These are the tiny components that make up the protein. The formation and regeneration of keratin structures is carried out by specialized cells that provide protection and renewal in hair, nails and skin.

The most important of these is called cysteine. It makes up around 17.5% of your hair. Why is it so important? Because cysteine contains sulfur - and this sulfur helps form tiny "bonds" called disulfide bridges . These bridges are like the superglue in the hair: they hold the keratin strands firmly together and make the hair strong, dimensionally stable and resilient.

Keratin is generally quite robust. It doesn't "break down" easily and can take a beating. Moreover, the keratin building blocks in the hair do not lie around chaotically, but are rather like threadsthat come together in bundles - similar to a rope: many thin fibers together make something really strong. The better these bundles hold together, the stronger, more elastic and more resistant your hair is in everyday life (e.g. when brushing, styling or rubbing against clothing).

Keratin therefore ensures that your hair can stretch without breaking directly, and that it is less susceptible overall. If the keratin structure is damaged (e.g. by heat, bleaching, aggressive chemicals or a lot of friction), the hair loses its stability more quickly. Products with keratin can penetrate deep into the hair fiber to strengthen the hair from the inside and optimally fulfill its role as a protective and structural protein.

Disulfide bridges: The "super glue"

Think of disulfide bridges as super-strong conductors that firmly connect the individual keratin fibers. They give the hair its shape and tensile strength. These bridges also protect the hair from external influences, helping to maintain its structure and resistance.

• Intact bridges: Your hair is elastic. You pull on it and it springs back.
• Broken bridges: Your hair breaks off when brushed or becomes "rubbery" when wet.

Our Sins 'n Lashes hair serum (with peptides) is aimed precisely at supporting these structures.

The structure of hair: keratin layer by layer

Your hair is not just a solid block. It is built like a well-insulated cable with three main layers, each representing a separate area of the hair structure:

• The cuticle (cuticle layer): This is the outermost layer. It consists of small keratin scales that lie on top of each other like roof tiles . This layer protects everything underneath. A good hair serum can help to make the surface appear smoother - the hair feels softer and looks shinier.

• The cortex (fiber layer): This is where most of the keratin is found - and also the dyesthat determine your hair color. This layer gives your hair its strength and elasticity. A lot of damage happens right here, for example through heat, bleaching, dyeing, friction and aggressive brushing. Care products cannot "rebuild" the hair, but they can help to protect the hair fiber , make it look smoother and visually conceal minor damage - especially in the lengths.
• The medulla (medullary canal): This is the inner "core". In very fine hair, it is sometimes barely present or missing altogether.

Why lengths and ends need extra care

Lengths and ends are the oldest part of your hair - they have already been exposed to the most everyday life, heat and styling. That's why they dry, split or brittle more quickly.
Products that are specially made for them help to prevent split ends, keep your hair smoother and better protect it from new damage.

The hair growth cycle & Keratin

Your hair doesn't grow at the same pace all the time. It goes through a cycle that resembles a change of seasons. Understanding which phase your hair is currently in is the key to preventing hair loss. 

Keratin deficiency & Hair damage: causes

Good hair care helps your hair to stay strong and healthy. It protects against things that damage hair in everyday life, such as heat, sun, friction and inappropriate care. Many products wrap around the hair like a thin protective film, smoothing the surface and helping the hair to dry out or break less quickly.

Nevertheless, many people ask themselves: Why do I have split ends even though I take care of my hair? Because keratin is very robust, but not indestructible. Every day, your hair is subjected to small stresses such as blow-drying, straightening, frequent brushing, UV radiation, chlorinated water, dry air or environmental pollution. Over time, the surface of the hair becomes rougher, the lengths become more sensitive and the ends fray. This causes split ends, even if you "actually do everything right".

Now comes the most important part: Here are the biggest enemies of your hair structure:

1. Heat styling (The final enemy)

Heat above 175°C is critical. Above this temperature, the keratin begins to denature (it melts internally). The hydrogen bonds break and the hair loses its shape. Professional keratin treatments consist of several steps, including blow-drying and straightening the hair. The blow dryer is an important part of this as it helps to smooth the hair and give it a long-lasting shine.

2. Chemical maces

Bleaching and perming only work because they forcibly break the disulphide bonds. This is pure stress for your hair. Without a subsequent protein treatment, the hair remains straw-like.

3. Environment & Summer

The sun is one of the biggest stress factors for your hair in summer. UV rays can cause hair color to fade faster and at the same time attack the outer layer of the hair. This cuticle layer is like a protective coat: If it becomes rough or "opens up", the hair loses its shine more quickly, feels dry and becomes brittle more easily.

Water can also become a problem in summer. Chlorinated water can also dry out the hair and make the surface look dull. Salt water draws moisture out of the hair and often makes it rougher, especially in the lengths and ends.

The result is often: more frizz, less suppleness and a higher risk of split ends.

4. Nutritional deficiencies

Your hair needs "food". A lack of iron, biotin or proteins causes your body to cut back on keratin production. Your individual nutrient requirements are crucial for the health and strength of your hair. Keratin production decreases with age, which can also affect hair structure and resilience.

The result: Thin, weak hair.

Many people only think of shampoo and serum when they think of 'hair care', but the most important part often happens on the inside. And yes: this doesn't just apply to your scalp hair. Eyelashes are made of the same basic material as hair, which is why the nutrition tips in this article also apply 1:1 to the hair on your head: Nutrition tips for healthy and long eyelashes.

How keratin affects hair shine & Strength

The quality of your keratin directly determines how your hair looks and how healthy it is. Keratin plays a central role in the health, strength and resilience of your hair. The most important benefits of keratin include the revitalization of the hair in depth, the increase in shine and suppleness as well as the strengthening of the hair structure. Deep conditioning strengthens the hair from the inside out, resulting in more strength, firmness and elasticity. Keratin also helps to reduce the appearance of split ends, ensuring long-lasting suppleness and resilience.

• Shine: Comes from an intact keratin surface that reflects light.
• Elasticity: Comes from stable disulfide bridges on the inside.
• Thickness: Depends on the protein density in the cortex.
• Color strength: A healthy cuticle protects the pigments from fading.

Tip: Read our article on hair growth hair oilto understand how you can care for your lengths and ends without weighing them down:

Hydrolyzed keratin vs. natural keratin in comparison

Maybe you've read "hydrolyzed keratin" on shampoo bottles before. Is that better? Different?

Normal keratin consists of huge molecules. If you just slathered it on your hair, it would be too big to penetrate. It would just slide off. That's why scientists use hydrolyzed keratin. This means the protein has been broken down into tiny pieces (peptides). These are small enough to penetrate deep into the hair shaft and fill gaps from the inside. Studies show that such peptides can increase moisture in the hair by up to 19% and reduce water loss by 30% !

Innovative formulas in keratin shampoos and conditioners are suitable for all hair types and strengthen the hair in a special way by making it softer and smoother. The range of keratin products is diverse and covers different areas of hair care, so there is a suitable product for every need.

Your new keratin hair care routine

You don't have to be a chemist to get the best out of your hair. Hair serums and hair oil are real must-haves in any care routine, as they are suitable for all hair types and perform a variety of functions - from intensive moisturizing and shine enhancement to protecting lengths and ends. These products are enriched with valuable oils and active ingredients that penetrate deep into the hair fiber, promote suppleness, support the smoothing of the hair structure and strengthen the strength and health of your hair. Hair serums are particularly indispensable in the field of hair care in order to cover the individual needs of your hair type and specifically address the needs of lengths and ends. They can help to reduce split ends up to 90 % and ensure a strong, smooth and shiny result.

For correct application, you should use hair serums sparingly and apply to wet, towel-dried or dry hair as required. This way, you won't weigh your hair down and achieve optimum care effects. Make sure to apply the products specifically to the lengths and ends to protect and repair these areas in particular. To ensure your hair serum doesn't weigh you down and you get maximum results, use our Hair Growth Serum Guide.

Here is a simple plan on how to protect and repair your keratin structure:

Step 1: Cleanse gently (protect the microbiome)

Use mild shampoos. Aggressive cleansers wash away the natural sebum that keeps your keratin supple and protects the scalp microbiome.

Step 2: Use the power ingredients

Look out for these ingredients in your products, they are keratin's best friends:

• Biotin (vitamin B7): The engine for amino acid metabolism.
• Peptides: The building blocks for repair.
• Panthenol (provitamin B5): A moisturizing magnet that thickens the hair.

Hair serums and other hair products are often enriched with high-quality active ingredients and nourishing oils that specifically address the needs of all hair types and can be used in various areas of hair care. These products offer comprehensive care and are suitable for everyone, regardless of hair type or texture.

Step 3: Seal & Protect

After washing, the scales are often slightly open. A cold rinse or a leave-in product helps to close the cuticle again. Special hair serum products have been developed specifically for the hair surface and to care for the hair lengths. They coat the hair fiber, smooth fine hair cracks, increase suppleness and protect both the lengths and ends from external influences. These products support the smoothing of the hair structure and ensure a healthy, shiny appearance. And very important: Never blow-dry without heat protection!

FAQ: Frequently asked questions about keratin & Hair care

Scientific sources & References

Transparency is important to us. This article is based on the following studies:

1. Rogers, M. A., Langbein, L., Praetzel-Wunder, S., Winter, H., & Schweizer, J. (2006). Human hair keratin-associated proteins (KAPs). International Review of Cytology, 251, 209-263.
2. Barba, C., Méndez, S., Roddick-Lanzilotta, A., Kelly, R., Parra, J. L., & Coderch, L. (2008). Cosmetic effectiveness of topically applied hydrolyzed keratin peptides and lipids derived from wool. Skin Research and Technology, 14(2), 243-248.
3. Kelly, R., Gu, J., Lim, J., Lati, E., & Manna, V. (2024). Effect of keraGEN IV keratin oral supplementation on hair, skin, and nail attributes. HealthMED, 18(2), 35-45.