Hygral fatigue and moisturized hair.
This is a very controversial topic, especially with the curlies. Now we are really getting into the bullshit marketing. The big challenge here is that scientists and hairdressers are not writing the copy ads for hair care. That’s what marketers do; rarely are they knowledgeable in hair care and science. They have convinced consumers that they need more moisture. The reality is that hair has very little water in it. We actually use amino acids and proteins in formulations to “moisturize” the hair by making it softer and more pliable. Counterintuitively, consumers feel like their hair is more moisturized if the water content is lower?? There is a famous study by MG Davis and S. Stofel on this. This is a formulator's trade mag write-up on water content in hair that mentions the study with lots more info on the matter. https://www.cosmeticsandtoiletries.com/testing/method-process/blog/21837786/measuring-the-water-content-of-hair.
Now, for hygral fatigue, we know the hair is responsive to pH because that’s how we color it. The higher the pH, the more the hair swells, opening up the cuticle. Here is a cool article talking about pH in shampoo and its effects on hair. https://journals.lww.com/ijot/fulltext/2014/06030/the_shampoo_ph_can_affect_the_hair__myth_or.4.aspx. This study shows that coconut oil can penetrate the hair. Coconut oil is hydrophobic and keeps water out of the hair. The hair was shown to have less damage and swelling because the oil was keeping the water out of the hair: https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=f6a1b75a588d6638e5790ea8829dfe109acc4023.
It is controversial to say “hygral fatigue,” which was adapted from a study on wool. Wool does swell when it absorbs water. Wool is very similar to human hair; it’s all keratin. The difference is that wool has more disulfide bonds, and it’s stronger. So the more scientific term would be to say the pH of water shows effects on the positive and negative charges of human hair, but that’s a mouthful. And honestly, if we wanted to cause no “hygral fatigue,” we would have our pH at 3.67. That is the pH of hair. We found that 4.6-4.7 pH is a sweet spot for the scalp's acid mantle, and not being so acidic, it irritated the scalp. After all, we treat the scalp first, always.