Maddie’s A Mad Scientist…You really got me into looking into my beauty products. The thing is that I’m also a chemist and a pharmacologist, so I do get a kick out of “hunting down the molecules” of my beauty products… there’s only one problem, I need some facts!! How small does a molecule have to be to effectively penetrate the hair’s cuticle and how large does it have to be to be able to effectively form films on my hair strands?
The Right Brain‘s Right With Her:
Thanks for the question Maddie. It’s especially rewarding to know that some of our readers have a scientific background.
Your question is not a simple one to answer hair penetration is not soley related to the size of the molecule. Size does matter (if you catch our drift) but so do other properties of the molecule. One of the most important factors to consider is the molecule’s affinity for the different regions of the hair that it might penetrate through. That’s because chemicals with the correct structure can diffuse through the Cellular Membrane Complex (or CMC) of hair. For example, coconut oil has been shown to penetrate hair. Coconut oil is a reasonably large molecule with a Molecular Mass of several hundred atomic mass units.
Likewise, what is and isn’t a film former is partly dependent its composition. For example in the case of proteins, somewhere above 2000 atomic mass units these polymers become effective film formers. But take this information with a grain of sodium chloride because it depends on the nature of the molecule, not just its molecular mass.
In case this isn’t a very satisfying answer and you’ve still got scientific thirst that needs slaking, go check out this article from Journal of the Society of Cosmetic Chemists for more. We hope this helps, we’re always glad to aid a fellow geek.