This is concerning the protein treatments like masks/deep conditioners.
As you already know, our hair consists of proteins, especially keratin, and keratin treatments are seen as the holy grail of hair care. Although there is a similarity, this doesn’t mean that it works better than other conditioning agents.
If an ingredient wants to bind to the hair, it needs to have an affinity with the hair. For example, in electrostatic interactions, the hair is negatively charged so it needs to bind to something which is positively charged or by a similar chemical structure like protein.
Hair can be damaged in two ways:
- The surface of the hair can be easily damaged (by brushing, or heat styling) and this gives a coarse feeling to the hair. This surface layer is the protective layer of the cortex. The cortex determines the strength of the hair and this cortex can be easily destroyed by perming, bleaching, etc.
Conditioning agents attach temporarily to the surface layer of the hair and smoothen the surface, but the cortex responsible for the strength of the hair is not repaired.
Proteins need to be differentiated by size:
1. High molecular weight proteins: these proteins cannot penetrate into the cortex of the hair and can only attach to the surface. They absorb onto the surface and form a protective film. This helps to smoothen the hair shaft (just like other conditioning agents).
2. Low-weight molecular proteins (hydrolyzed keratin, hydrolyzed silk, or amino acids like alanine): These proteins are smaller and could potentially penetrate the hair shaft and strength the hair.
Not all hydrolyzed proteins can penetrate into the hair shaft and the affinity of the protein with the hair keratin needs to be good enough to really bind to the hair. As the hair keratin has a very unique composition, it is not very likely that a standard hydrolyzed protein will be able to do so.
To summarise, high molecular proteins are just like other conditioning agents and form a film or protection around the hair cuticles. Hydrolyzed proteins are more better regarding improving hair strength.