I have said all of this regarding oil shampoo and oil penetration of hair, on LHC. My posts there are copyright protected as are my posts in this blog. Linked sources, and partial quotes in this blog are from websites which anyone can access.
Someone once asked me about the 2003 research, the one "everyone" including scientists quote that shows that coconut oil can penetrate hair the deepest, compared to other oils. I was asked if I thought the research study was biased, since it was funded by a company that sells vegetable oils. My reply at the time was that it is a peer-reviewed study. To me, the results are accurate.
However, after rereading the research study, I realized that the hair had been prepped or prepared, with an emulsifier first to remove oils and then washed with SLES (sodium laureth sulfate), to make sure nothing could prevent any of the oils from penetrating hair.
In the 2005 study, on hair penetration and heat being used, the hair preparation is unclear to me. However, what is clear is that the cuticle scales are clear to the researchers in measuring what if any oils remain on the hair surface, or are visible. That means to me that absolutely nothing was on the hair that could obstruct any of the oils from penetrating it, in as much as the researchers could do to make that so.
I have no issues with the research studies. What they did not address was that in real life today, many shampoos and conditioners coat the hair and do obstruct the lauric acid in coconut oil from penetrating hair.
If this were not so, the results the movie stars in those articles I wrote about regarding oil shampoo had, hair with volume and curls and waves, with no tangling, when no conditioner had been used afterward and no styling aids either, just acidic rinses, would be the same results that anyone who tried any coconut oil shampoo would get.
That did not happen and I realized why. The coatings that exist today in products did not exist then. The coatings that did exist like certain botanicals were not widely used in soaps or the shampoos available then, like today in "all natural" hair products.
Coconut oil used over conditioner can cause dry "crunchy" ends. It is not going into the hair one bit. It is just sitting on top of the conditioner, which can be nice though, if there is also no product residue on the hair. No oil mixed with conditioner, or a butter on unclarified or clarified hair is going into the hair. They can make very nice surface conditioners only.
Even herb washes coat the hair and no results like those of the movie stars have been reported by people using coconut oil as a pre-wash before a herb wash that I have read anywhere.
It is as simple as that. Some coatings in shampoos today do allow lauric acid to penetrate hair. That is the biggest issue with oil shampoo, finding those shampoos and finding a clarifying shampoo that does not leave barrier coatings behind. Superfatted soaps can also create problems for an oil shampoo and lauric acid penetration. Extra, double bond oils, which can also be drying oils and cause tangling, or butters, which contain waxy stearic acid, choke off lauric acid access to the hair. Only a small amount of lauric acid can access hair without barrier coatings present.
Concerning coconut oil used as a grooming aid reducing protein loss from combing, the same thing applies. It would need to be used on bare hair for that benefit, like in the research. Used over coatings, it has no direct access to the hair. The protein loss coconut oil can help prevent is from the hair cuticles. Conditioner can help do that too or any coating on the hair that helps prevent friction, like mineral oil, which can do so better than conditioners, vegetable oils and silicones.
Protein treatments can penetrate hair, well clarified hair best, as directions on packaging often indicate and they can wash out easily, easy in, easy out.
When coconut oil lauric acid deeply penetrates well clarified hair, it bonds with protein in the hair cortex and while it can be washed out too, it tends not to be washed out as easily as protein treatments. Note: Most fractionated coconut oils contain no to almost no lauric acid. They are not suitable to be used to achieve this result.
Why was the research conducted? Here is the answer from your Page 3 or Page 177 of the study. Colour added by me.
"Prolonged use of coconut oil has been known to lead to healthy looking long hair, suggesting that it may prevent damage to the cuticle in grooming procedures involving abrasion. Obvious is the lubricating effect of oil on fiber friction, which reduces abrasive damage, especially in combing. However, in modern times, the trend in hair oil formulations is more towards the use of non-sticky oils such as mineral oil ..."