Hair Cuticles Don’t Work Like We Think They Do

I learned that what we think about the cuticle and water is wrong. The cuticle of virgin hair is not an impenetrable barrier that locks water out; water actually diffuses past the cuticle within minutes. Sounds unbelievable? Well, it’s true, and it shows just how wrong we’ve all been taught by the internet.

On a slightly different note, the facts that I’ve learned about the cuticle put a big kink in the porosity theory. Personally, so far I believe it’s completely wrong, at least the “low porosity” side of it.  All evidence points to the fact that any virgin undamaged hair type gets plenty of moisture in and we don’t need to be trying to force water in. In fact, other natural proteins with ratios of crystalline versus amorphous proteins are similar to the hair’s ratio show very similar robust water absorption [2]. But anyway, more on that later.  Let’s get back to the cuticle and how it’s not as water-proof as we were taught.

Where did we go wrong?

I’m curious where this incorrect fact came from.  Part of it must be our own intuition about moisture.  We feel rough hair and assume it’s dry because that’s how our skin feels when it’s dry.  Except, we’re fooled by our senses (see my post on the perception of moisture for more details). The other part is that we’ve been taught that the cuticle is this dense, hydrophobic fortress that doesn’t allow anything in. My personal theory is that this came from the hair styling world––in particular, hair dying.

Hair colorists have known for decades that hair dye can be hard to get into hair. That’s why highly alkaline chemicals are used to help the hair strand swell and let more of the dye molecules in.

“The cuticle does have a mechanical protective role for the rest of the fiber, and acts as an important barrier to dye sorption by the fiber.” -Feughelman, 1982

Studies as far back as the 80’s showed how stripping the hair of its cuticle allowed more dye in. I would bet this is where the confusion comes from because we have forgotten a crucial detail: dye molecules and water molecules are different. Did you notice how the quote from the study said dye sorption? Not water sorption; dye sorption.

In terms of water, scientists say that hair absorbs water easily, it’s the bulkier dye molecules that have a hard time penetrating the hair.  However, that fact has gotten lost over time, buried under years’ worth of blog posts that incorrectly state that the hair cuticles shut water out.

Reference:

1. Feughelman M. The physical properties of alpha-keratin fibers. 1982.
2. Hailwood AJ, Horrobin, S. Absorption of water by polymers: analysis in terms of a simple model. Transactions of the Faraday Society. 1946;42, B084-B092.