Keratin is one of the most common ingredients in hair care marketing, and one of the most misunderstood. The confusion usually comes from conflating two very different things: keratin as a structural protein in the hair shaft, and "keratin treatments" applied in salons. They share a name but work in entirely different ways.
What Keratin Actually Is
Keratin is a fibrous structural protein. It is the primary material that makes up hair, skin, and nails. The hair shaft itself is approximately 95% keratin, arranged in overlapping scales along the cuticle layer. When these scales are smooth and flat, hair reflects light evenly and feels soft. When they are lifted or damaged, hair appears dull and feels rough.
The keratin in your hair is produced by cells called keratinocytes in the hair follicle. Once the hair shaft emerges from the follicle, it is entirely made of dead cells, which is why it cannot repair itself from the inside. Any improvement to the shaft has to come from the outside.
Keratin in Shampoo and Conditioner
Hydrolysed keratin, form used in shampoo and conditioner formulas, is keratin that has been broken down into smaller fragments (peptides and amino acids) through a hydrolysis process. These smaller molecules can adsorb onto the surface of the hair shaft, temporarily filling gaps in the cuticle and smoothing the surface.
The key word is temporarily. Hydrolysed keratin in a rinse-off product like shampoo or conditioner does not permanently bond to the hair structure. It coats and smooths. Each wash cycle applies a fresh layer, which is why consistent use matters more than single application.
Does It Weigh Fine Hair Down?
This is the right question. The concern with fine hair is that heavy conditioning ingredients, like silicones and certain oils, deposit on the hair shaft and add weight, reducing volume and causing roots to flatten faster.
Hydrolysed keratin behaves differently. Because the peptide fragments are small and water-soluble, they do not accumulate on the hair the way silicone-based conditioners do. They adsorb to the surface, provide smoothing and temporary strength, and rinse away without heavy residue. For fine hair, this makes keratin a more appropriate protein source than heavier film-forming ingredients.
The relevant variable is molecular weight. Lower molecular weight hydrolysed keratin penetrates closer to the cortex; higher molecular weight fragments coat the surface. Most hair care formulas use a blend. Neither tends to add meaningful weight to fine hair strands when used in appropriate concentrations.
Keratin Treatments vs Keratin in Hair Care
Salon keratin treatments, metimes called Brazilian blowouts, work through a completely different mechanism. They use high heat and, in many formulations, formaldehyde or formaldehyde-releasing compounds to cross-link keratin proteins onto the hair shaft. The result is a semi-permanent structural change that lasts weeks to months.
These treatments carry real risks for fine hair: the heat and chemical process can cause brittleness and breakage in already-delicate strands. They are not comparable to using a keratin-containing shampoo or conditioner, which involves no heat, no formaldehyde, and no permanent structural change.
Our BLOOM BATH Shampoo and BLOOM BALM Conditioner use hydrolysed keratin as part of a COSMOS certified formula designed specifically for fine hair, providing protein reinforcement and cuticle smoothing without silicones or heavy film-formers. The full Volume and Body collection is built around this approach.
Related reading
- How to Add Volume to Fine Hair (Without Weighing It Down)
- Botanical Proteins for Hair: What the Science Says
- How to Repair Damaged Hair (What Actually Works)
- Olaplex Alternatives That Are Actually COSMOS Certified
Frequently Asked Questions
Is hydrolysed keratin the same as a keratin treatment?
No. Hydrolysed keratin in shampoo and conditioner is a water-soluble protein fragment that temporarily smooths and strengthens the hair surface. Salon keratin treatments use heat and cross-linking chemistry to create semi-permanent structural changes. They share the word keratin but work through fundamentally different mechanisms and carry different risk profiles.
Can fine hair use keratin products?
Yes. Hydrolysed keratin is generally well-suited to fine hair because the protein fragments are lightweight and water-soluble, unlike silicones or heavy oils that can deposit and reduce volume. The suitability depends on the full formula: a product with hydrolysed keratin but also heavy silicones will still weigh fine hair down.
How often should I use keratin shampoo for fine hair?
Frequency depends on your hair and scalp type. For fine hair, washing two to four times per week is common. There is no risk of protein overload from a rinse-off keratin shampoo under normal use conditions, hydrolysed protein coats and rinses, it does not permanently accumulate.
What is "protein overload" and does it apply to keratin shampoo?
Protein overload is a term used in hair care communities to describe hair that becomes stiff and brittle after heavy use of protein-based leave-in treatments. It is associated primarily with high-concentration leave-on protein treatments applied repeatedly without adequate moisture. Rinse-off keratin shampoos and conditioners used at normal frequency are not typically associated with protein overload because the contact time and deposit amounts are much lower.
Does COSMOS certified keratin exist?
Yes. Hydrolysed keratin can be sourced and processed to meet COSMOS standards, which require that the ingredient comes from a natural source and is processed using approved methods. The keratin used in COSMOS certified formulas is typically derived from sustainably sourced animal or plant proteins and processed via hydrolysis, COSMOS-approved transformation method.