The final part of this series covers a quite unexpected water helper - hydrolysed protein. Please remember that hydrolysed protein is quite special. Do see this previous post which describes the difference between amino acids, proteins and hydrolysed protein (click here).
So on to the main course - In one particular experiment, hair treated with hydrolysed wheat protein and then immersed in water, took several hours to dry back to its 'normal' water level compared to untreated hair which took just 4 minutes (J Cosmet Sci, pg 69-87, 1993).
What does this mean? In moisture terms, it means that
1. Hydrolysed protein delays the exit of water from hair
2. Hair treated with hydrolysed protein will retain moisture for longer
Further studies revealed that hydrolysed protein can actually penetrate hair (J Cosmet Sci, pg 193-203, 2000). The extent of this penetration varies with how damaged the hair is. Damage could mean old hair at the tip or damage due to bleaching/relaxing. The more damaged the hair, the more the penetration of the hydrolysed protein.
I have not read the curly girl book by Lorraine Massey but I did read a review somewhere (can't remember where) which was critical of the inclusion of protein as a necessary conditioner ingredient. Looks like it may be quite useful! (Any curly girl readers who actually have the book - do let me know if this was actually stated in the book!)
Also, because I don't like to waste research, the same effect has been found with hydrolysed keratin (wool) on skin.(Skin Res Technol, pg 243-248, 2008 and J Cosmet Sci, pg 99-107, 2007).