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Ken and his plastic hair. One of the greatest differences for medium to coarse hair vs. fine hair is an element of flexibility. In cosmetics science, it is sometimes called plasticity. This isn’t about plastic hair (but I can’t resist a photo of Ken, Barbie's anatomically ambiguous "friend"). Oils, conditioning agents like cationic quaternary surfactants (your conditioner probably has them), fatty alcohols like cetyl alcohol and “butters” like shea butter and silicones all add plasticity to hair. So might proteins, amino acids and humectants. ©Science-y Hair Blog 2013 When we think “plastic” in everyday life, we usually think of hard or semi-hard plastic boxes and containers. But in biology, physics and engineering, “plasticity” means the object in question has flexibility, it can be molded (deformed) and is pliable. In this post , I suggested that one of the troubling issues for fine hair is that it can have an excess of plasticity – it is very easily deformed. ©Science-...

The Good, The Bad, The Weird (And the extremely long-winded post) Here I’m referring to 2 classes of chemicals: quaternary cationic surfactants and cationic polymers. First off, cationic means something has a (net) positive charge (+). Hair has a net negative charge at the pH environment in which it usually exists (somewhere between pH 4.5 and 5 is average). This charge is mostly because of it’s composition, although damaged hair has more potential bonding sites (negative charges) than less-damaged hair. I fear I’m about to give the impression that these ingredients are bad for your hair. They are not, in fact, they are responsible for silky, smooth, lustrous hair that holds a style. They help define waves and curls and protect damaged hair/protect hair from damage. They can prevent flyaway hair and the high fluff/frizz factor that comes with wavy and curly hair. What? You have straight hair that frizzes? Then no, you don’t have completely straight hair – you have some waves. These in...