Wednesday, March 28, 2012

How Coarse Hair is Different

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-y Hair Blog 2013
Hair which is coarse (the diameter of the hair shaft), or which has a determined wave/curl to it, resists deforming under a load. It is not as super-flexible as fine hair. Hair which is kinking – has little bends and twists of the actual hair shaft, not just a simple, general curling habit, also tends to lack plasticity. So fine / medium hair and coarse hair are very different fibers. Kinking, curly fine hair and curly fine hair without kinks are quite differently-behaving fibers. Fundamentally, they are made from the same ingredients, but the expression of the ingredients is different.

If hair is low on plasticity, it is difficult to change it’s shape – hard to curl straight hair, hard to straighten curly hair. It will tend to feel thick and strong rather than silky. It will behave differently in a variety of situations and to a variety of treatments. It may not want to lie smoothly, which is a prerequisite for shine.
Fine hair, like coiling up cotton rope,
bends willingly

Medium to wide hair resists bending,
rather more like coiling up a garden hose.

Coarse hair has more internal support than fine hair. It holds it’s own shape quite well, it is less likely to be weighed down. It isn’t easily dented by ponytail holders and bobby pins. You can see in the graphic (below) how much more brown (hair cortex) there is with a wider hair than a narrower (fine) hair. This is why wider hairs are less pliable. I like to imagine fine hair like trying to wind or coil up a cotton rope and wide hair like coiling up a garden hose, which resists the bending and tends to want to coil in it’s usual pattern. 
See notes to the right. I know - hair is elliptical. But this is easier
for me to "draw!"

In the fine hair post, this visual aid represented the problem of how much more conditioner or oil clings to fine hair vs. wider hairs, relative to the mass or volume of the interior of the hair. It works the other way around for wider hairs or kinky hairs – plenty of conditioner is needed to make this hair type feel soft and smooth and bendable because the conditioner contacts so much less of the whole of the hair.

Plasticizers in hair work like lotion or cream on dry skin – soften, seal in moisture, or attract moisture. But they also add an element of pliability and flexibility (plasticity) that the hair may not have on its own. Like oiling leather or polishing a dry leather shoe, something inflexible becomes flexible, softer and glossier with the addition of a plasticizer (oil or shoe polish).
©Science-y Hair Blog 2013
So if you have ever used a leave-in conditioner, smoothed coconut oil or avocado into your hair, left in a lot of conditioner – and had your hair become softer, springier, better defined as a result – you can chalk that up to the increase in plasticity.

And if you want your hair to have more pliability, you need plenty of oil or conditioner – not only to act as an occlusive (prevent moisture loss because hair + water = flexibility), but also to help your hair stay soft and to align itself with its neighbors which increases shine and wave/curl definition.

If your hair has kinking in it (this occurs in wavy-haired people as well as curly-haired people, though it is most commonly thought of in hair with very tight curls), the added plasticity of oils and conditioners also helps prevent breakage. Each little bend and twist of the fiber (kink) can be a point of weakness in the fiber. The more abrupt a directional change, the weaker that spot is. Kinky hairs softened by plasticizers bend more readily – instead of breaking.
©Science-y Hair Blog 2013
Here’s a final thought. If you have fine hair, which is dry or porous or damaged, it may act like wider hairs and need more plasticity too, but fine-haired people can usually get away with much less.

Some parting thoughts: Usually you can tell if you have coarse hairs. They feel solid between your fingers. You can see them easily when held up against a contrasting background. When you bend coarse hairs, they like to spring back. Some coarse hair is quite pliable and bendable, some feels more rigid and wiry. Especially when hair is light-colored or not thick (densely packed) on your head or it is soft - it may not seem coarse when it actually is. It is a myth that all coarse hair is rigid or feels wiry. Coarse hair can be slippery and silky or springy and soft, or wiry.


  1. I debated asking this in this comment section vs the one on fine hair, but since you mentioned it here, I'll proceed. I understand that fine hair generally can tolerate protein much more effectively than medium to coarse hair. Here you noted the differentiation between fine curly hair that kinks vs fine curly hair that does not, since the kinking hair would best benefit from increased plasticity. So my questions: Does use or frequency of protein change in any way for fine kinking hair? I am particularly curious about hair of African descent, since I know a lot of people call it coarse, but very typically it is fine in nature, just has a kink to it. When considering protein/moisture balance and African hair, would it simply make more sense to focus maintenance efforts on a balanced approach, that is, equal parts protein and moisture (lightweight emollients for plasticity)? I am making a speculating leap of understanding that kinking in the hair means both low *and* inconsistent protein content along the length of the strand. And also, how might porosity come into play here...would generally healthy kinking hair present as porous or nonporous hair? This is getting long, but I understand that protein and moisture content is on a continuum, respectfully, and am wondering where this type of hair would sit on that continuum. So for example, if fine hair is 1 (frequent protein use, not a lot of emollients) and coarse hair is 10 (more emollients, less protein use), where does fine kinking hair sit? 4? Or perhaps 6? Thank you for your content and time!

    1. Hello TW,
      I agree with you - with fine, curling and kinking hair you have to use oils and conditioner (or oil in conditioner) when you use protein to keep hair flexible. That can mean using oil-and-conditioner-rich products with protein in them, or always following up protein-containing products with a deep conditioning treatment or an intense conditioner. There is always a lot of experimenting to do to find out which proteins work better, how long to leave protein on. I think it better to err on the side of caution and leave protein on for shorter periods of time when there is any question of whether or not protein will cause any unwanted side effects.

      The more porous hair is, the more it is likely to benefit from protein. That's an issue of protein having more ability to bond to porous hair. As you noted - those more-porous areas *also might* grab on to too much protein. In that case, working with smaller proteins like Hydrolyzed keratin, Hydrolyzed silk, amino acids, maybe Hydrolyzed collagen and low molecular weight Hydrolyzed wheat protein, is a good idea. Those proteins are less likely to create stiffness or a dry, brittle feeling in hair.

      On your numeric scale, fine, normal porosity or low porosity hair with kinking is probably around 5. Fine, porous hair is going to be between 6 and 10, depending on your climate, how dry hair feels, whether or not you have hard water (which can make hair feel rigid).

      There is a benefit of protein creating a bit of rigidity for fine hair - in that it gives finer hair some support, a little more substantial feel. That's not crossing over into "dry, brittle" territory, but when you've got the right protein for your hair and a good combination of protein and conditioning, finer hair feels so much more like strong, individual fibers thanks to the support from the protein.
      I hope that helps! I'm a bit behind on responding to comments.