Which is best for our hair?
So, we have established that all of these butters and oils are made up of different mixtures fatty acid molecules. What specifically accounts for the varying preferences expressed by consumers? Some curly-haired people extol the virtues of butters, while others adamantly proclaim oils as their holy grail ingredient.
The major components of butters and coconut oil are one or more saturated fatty acids, while the major components of most oils are a mixture of mono- and polyunsaturated fatty acids. One must assume that the differences in performance when used as emollients for the hair are a direct result of these differences in molecular structure. This is exactly the reason, and the science is fairly straight forward.
You will recall recent discussions we have had regarding the nature of the cuticle layer of the hair. Pores in the cuticle layer (whether from damage or from its being slightly open due to being wet) allow passage of some molecules into the cell membrane complex layer that is just beneath the cuticle scales. The fatty acids in this lipid layer act as a diffusion port that allows some fatty acids to penetrate the hair shaft. However, due to molecular structure and geometry, not all fatty acids are created equal in their ability to diffuse into the hair.
Generally, molecules with a straight chain geometry (saturated fatty acids), such as stearic acid, lauric acid, and palmitic acid can easily fit through the pores of the cuticle layer and slither through the CMC and into the interior of the cortex. Recent spectroscopic studies have allowed scientists to confirm that monounsaturated fatty acids are also able to readily penetrate the interior of the hair via this route. However, polyunsaturated fatty acids seem unable to penetrate into the interior of the hair at all, and remain either adsorbed onto the exterior surface of the hair or may get wedged into the cuticle layer.
Fatty acids in the interior of the hair can provide brittle hair with much-needed suppleness and elasticity. However, porosity is a very important factor to consider when using easily absorbed oils and butters. If one has very porous hair, it can absorb excessive quantities of these oils, which can lead to a host of problems. Among these could be greasy feel, dull appearance, limp hair, a swollen and open cuticle, frizz, and tangling. It can be very difficult to remove excess absorbed oils, in my experience, requiring the use of harsh surfactants, which strip the hair of its own lipids.
Oils high in polyunsaturated fatty acids may provide ease of wet combing and prevent static build up and fly-away hair. In addition, they form a barrier film on the surface of the hair, preventing moisture from escaping the interior of the hair. However, they might contribute to hair that feels greasy or sticky to the touch. Oils on the surface of the hair can also attract dirt to your hair. Another potential concern is that if these types of oils are indeed wedged into the cuticle layer at all, hair becomes vulnerable to the dangers of having a raised or rough cuticle.
My recommendation is to try small quantities of different oils and butters and carefully observe your results and preferences. Then, when you find things you really like or dislike, look into the fatty acid composition of the things you tried. This will help you determine if your hair needs saturated, monounsaturated, or polyunsaturated fatty acids, and you can then choose your products accordingly, armed with your knowledge of the underlying chemistry!