The water content in human hair, or hair moisture levels, is very important for its cosmetic properties and general health. Lacking moisture for an extended time will result in dry, brittle, tangly and easy to break.
Talking about hair hydration, most of us could easily get the picture. However, to gain satisfactory results from your hair moisturising effort, it is beneficial to get in-depth information on diverse aspects related to this topic.
This article sets out to help you understand how the hydration process triggers its influence on the hair and which factors can impede it. Also, you will learn several signs that your hair requires more hydration and how to do it properly.
- Niacin for Hair: How to Regain Strength
- Hair Health During Pregnancy And Postpartum Period
- Turmeric (Curcumin) Hair Loss: What Science Says?
The structure of human hair and how water impacts it
The hair shaft, the part above your scalp, contains three main layers, naming the medulla, cortex, and cuticle.
(Source: In Vivo Human Hair Hydration Measurements by Using
Opto-Thermal Radiometry, Bontozoglou et al. 2019)
The medulla, the innermost layer made of soft keratin, acts as the core of the hair shaft. It is soft, fragile, and amorphous in appearance. This layer may even be completely absent in some cases (e.g., in naturally blonde or fine hair).
The middle and thickest layer is the cortex, composed of spindle-shaped cortical cells. This layer constructs the main body of the hair, and unlike the medulla, it is made of hard keratin. The cortex layer contains pigments. It gives the hair its strength and also determines the hair colour, curls pattern, thickness, and texture. More importantly, it is the predominant layer of water absorption in hair.
Lastly, the outermost layer of the shaft is the cuticle, consisting of scales of hardened, keratinized tissue. It is a thin, translucent coating surrounding the hair shaft. This layer often has the imbricate pattern, which resembles the layout of tiles on a house roof, covered with a layer of lipids that helps the hair repellent to external water sources and retain moisture within the hair.
Also, the cuticle has a critical role in shaping the hair porosity - the ability to let in and retain moisture of your hair. When the structure of the cuticle is too close together (low porosity), it hinders the penetration of hair and oils. Meanwhile, if the structure is too widely spaced (high porosity), it is harder for the hair to keep the moisture within.
That is to say, in the hair shaft, water (and other compounds) penetrate deeper through the filter of the cuticle layer, whilst the moisture level of your hair is determined by the water content existing in the cortex layer.
On average, hair fibres contain up to 32% of water, and this figure could change significantly depending on diverse external factors, such as humidity, sunrays, temperature, or chemical treatments. When hair is exposed to water, it swells constantly and becomes softer. Your hair can take up to 30–35% water before being fully hydrated and becoming wet.
Meanwhile, hair hydration is the process in which water is applied and penetrates the cortex and medulla layers of the hair shaft, resulting in moisture provision and the hair's ability to absorb more water. Meanwhile, the cuticle with its lipid film will help lock the water within the inner layers, preventing moisture loss.
Once the hair is deprived of water or suffers from moisture deficiency, the hair elasticity or brittleness is altered, leaving it fragile and vulnerable to damage. Also, dry hair tends to absorb moisture from the environment, making it frizzy.
That is to say, besides the ability to absorb water, how the hair seals such moisture is also significant in maintaining an optimised hydration level for your hair. Hair hydration should include hydrating the hair and locking the moisture within. Otherwise, your effort could go to waste as the water content in the hair shaft remains unchanged, and your hair still stays dehydrated.
Influencing factors of hair hydration
First, the water content of hair depends largely on relative humidity (RH). One study found that the hair volume increased by 12.2%, 16.3%, and 24.6% when the RH reached 40%, 60%, and 90%, respectively. The hair weight could increase up to 22.6% when HR is 86%.
One other significant inhibitor to the hydration level of hair is chemical treatments. Reactive cosmetic hair treatments often impair fibre structure, resulting in adverse effects on water absorption. For example, hair bleaching often relies on an oxidizing agent whereby melanin and other components are oxidized. Thus, the treatment can readily transform the fibre surface. Dyeing, perming, or using harsh products can all influence hair porosity over time. Research shows that after straightening, the hair could become significantly dehydrated.
When the cortex layer is affected by heat or harsh chemical treatments, the cuticle scales are raised and open instead of laying flat and pointing towards the hair tip. This alteration, in turn, leads to the struggle of your hair in retaining moisture.
Prolonged UV exposure will also make your hair more porous. Moreover, ageing is likely to impact the hydration level of your hair. Indeed, research findings suggest that the hair at a younger age can hold water better while losing water much more slowly.
Does your hair need more moisture?
Recognise the hydration problem
As you already know, hair is unique among individuals. Thus, the hydration needs for hair vary, depending on the hair type, environment, lifestyle, and hair care regimen. How do you know if your hair has a moisture deficiency?
You can recognize moisture deficiencies when your wet hair feels rough, hard and tangly. When you pull the hair strand, it doesn’t stretch much before breaking. Due to the low water content within the hair shaft, it tends to lose natural elasticity.
In addition, hair that lacks moisture looks and feels rough and tough. It is more prone to breakage as it is super fragile. Dehydrated hair also takes more time to feel thoroughly wet in washing as it needs to absorb more water to be fully hydrated.
On the contrary, moisture-balanced, healthy hair is very resilient when wet or dry. It should feel soft and supple, move well and could be lustrous, sheen or shiny.
How to properly hydrate your hair?
Hair hydration is not a one-time treatment. It should be a continuous process with healing treatments and then maintenance. Anyhow, you need to understand your hair condition prior to thinking about how to improve its hydrating condition.
To hydrate your hair adequately, you might want to have a proper moisture hair care regimen that regularly supplies moisture for your hair. One option is to develop the habit of hydrating hair several times per week or whenever it feels dried out. However, if you realise that you have to apply hair moisturisers multiple times a day, you might be experiencing a porosity issue. Due to such an issue, your hair could not effectively retain the moisture applied and gets dehydrated constantly.
You might also need to look into which moisturiser products you add to your regimen. As water should be there in the ingredients list (well, there could not be any hydration without water!), watch out for heavy occlusive oils such as petrolatum. Their large molecules, trapped on the outside of the hair strand, coat the hair profusely and act as excellent moisture retainers. Research shows that film petrolatum could block more than 98% of the moisture from moving in or out of the hair.
That said, they also block all external moisture sources from taking effect. Because they are hard to be washed away, it could take several wash cycles or even strong cleansing actors to clear them up. Eventually, these oils deposit heavy films on the hair’s cuticle with regular use. Thus, they could obstruct all moisture from entering the hair’s fibres, resulting in chronic dryness.
On the other hand, lighter oils such as plant and seed-based oils form semi-permeable films on the hair cuticle. Moreover, they could quickly wear off from the hair’s surface or even penetrate and reinforce the hair fibre, leaving opportunities for re-moisturising efforts.
Also, ensure that you layer hair care products effectively for hydrating success. Don’t use oils before or without moisturisers as they will deter moisture from entering the hair strand, worsening the dryness. A light coating of oil on top of a moisturiser product is a beneficial method. By doing that, water is introduced to the hair fibre first and then locked into place with oil.
Last but not least, make sure you don’t overuse protein-based products such as hair repair or other leave-in treatments. Protein-rich products are beneficial for supporting the cuticle by filling up broken spaces and adding structure to the hair strand. However, cuticle repair can cause adverse effects through the overuse of products. The protein overload could bind strongly to the hair’s cuticle and undermine the water absorption ability of the hair shaft. Ironically, your hair is left dehydrated and damaged due to your excessive effort to repair it.
The information we provide is not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you have any concerns about your health, please consult your doctor.
Barba, C., Martí, M., Manich, A. M., Carilla, J., Parra, J. L., & Coderch, L. (2010). Water absorption/desorption of human hair and nails. Thermochimica Acta, 503, 33-39.
Benzarti, M., Pailler-Mattei, C., Jamart, J., & Zahouani, H. (2014). The effect of hydration on the mechanical behavior of hair. Experimental Mechanics, 54(8), 1411-1419.
Breuer, M. M. (1972). The binding of small molecules to hair I: The hydration of hair and the effect of water on the mechanical properties of hair. J. Soc. Cosmet. Chem., 23, 447-470.
Bontozoglou, C., Zhang, X., Patel, A., Lane, M. E., & Xiao, P. (2019). In Vivo Human Hair Hydration Measurements by Using Opto-Thermal Radiometry. International Journal of Thermophysics, 40(2), 1-11.
Egawa, Hagihara, M., & Yanai, M. (2013). Near-infrared imaging of water in human hair. Skin Research and Technology, 19(1), 35–41. https://doi.org/10.1111/j.1600-0846.2012.00651.x
Murthy, Wang, W., & Kamath, Y. (2019). Structure of intermediate filament assembly in hair deduced from hydration studies using small-angle neutron scattering. Journal of Structural Biology, 206(3), 295–304. https://doi.org/10.1016/j.jsb.2019.04.004
Yu, Y., Yang, W., Wang, B., & Meyers, M. A. (2017). Structure and mechanical behavior of human hair. Materials Science and Engineering: C, 73, 152-163.
Davis-Sivasothy, A. (2011). The science of black hair: A comprehensive guide to textured hair care.