You may have heard that hair is very fragile when wet, but do you know why? What’s the science behind this phenomenon? To help us understand, we consulted with a hair scientist with a Chemistry Ph.D.
This article dives into the science of wet hair and explains why it’s more vulnerable, what happens when hair absorbs water, and how you can protect it. Understanding these concepts can help you maintain healthier, stronger hair.
Understanding Hair Structure
Hair is a unique natural fiber made primarily of a protein called keratin. This protein forms microfibers arranged in unique patterns, giving hair its strength.1,2
Interestingly, the same keratin is found in sheep’s wool, making these two fibers quite similar in their physical and chemical properties.3 Like other natural fibers such as cotton and wool, human hair is porous, which can adsorb water molecules and cosmetic active ingredients.
Impact of Water on Hair
The water content in hair changes based on environmental conditions like humidity and temperature. When hair absorbs water, it significantly affects its strength, feel, and appearance.
For instance, higher adsorption of water molecules can make hair appear frizzy and brittle. Everyday activities like washing or showering expose excess water to hair, altering its properties. Wet hair is particularly fragile and prone to breakage during combing or brushing.
But why does this happen?
How Water Affects Hair Structure
Hair has tiny pores on its surface (the cuticle layer) that allow water molecules to pass through these channels to go deep into the cortex. Water molecules interact with the keratin structure by forming hydrogen bonds with the hydrophilic (water-attracting) amino acids.
Because water is polar, it breaks down the existing columbic ionic bonds inside the protein, causing hair to swell and its diameter to increase. The concentration gradient controls the degree of swelling, and the amount of water molecules adsorbed.
Under extreme conditions, this swelling can create pressure inside the hair shaft, sometimes leading to stress or damage, known as hygral fatigue.4,5
Why Wet Hair is Fragile
The strength of hair depends on the integrity of its structure, which is maintained by an extensive network of chemical bonds. Keratin, the main protein in hair, is held together by various types of bonds, including disulfide bonds, van der Waals bonds, and ionic bonds.
Water, being polar, breaks these ionic bonds. Although these bonds are weak, they play an important role in stabilizing the keratin structure. When these bonds break, the hair becomes weaker and more fragile.
Another reason wet hair is fragile is due to the swelling caused by water molecules inside the protein structure, creating osmotic pressure. Combing or brushing wet, swollen hair requires more force, increasing the risk of breakage.
Studies have shown that wet hair is harder to comb than dry hair, supporting the idea that swelling alters the surface properties of hair fibers, making them more difficult to manage.1,2,6,7,8
The Dangers of Sleeping with Wet Hair
Leaving your hair wet for a long time, or sleeping with wet hair, is not advisable. Prolonged exposure to moisture keeps the keratin in your hair swollen and fragile. During sleep, physical contact with a cotton pillow, bed linens, or even other hair strands can damage the outer layer of your swollen hair.
Additionally, leaving hair wet overnight can lead to an unpleasant odor. The humid conditions create an ideal environment for the growth of microbes on the scalp, which increases microbial activity and causes a bad smell. To avoid this, make sure to wash and condition your hair regularly, especially if you notice any odor.
How to Properly Handle Wet Hair
- Dry Gently: After washing, gently towel-dry your hair to remove excess water. Avoid rubbing, twisting, or tying wet hair as it can cause damage.
- Use a Blow Dryer: Use a blow dryer at a low temperature to dry your hair. Avoid using hot air on wet hair, as it can cause further damage by creating steam inside the hair shaft.
- Hair Care Routine: Don’t wash your hair daily; twice a week is sufficient. Protect your hair from rain by wearing a hat or scarf, and avoid sleeping with wet hair.
- Swimming: If you swim in chlorinated or salt water, wash your hair immediately afterward with an anti-residue shampoo and conditioner.
Tips for Maintaining Healthy Hair
- Use Conditioners: Regularly use both rinse-off and leave-in conditioners to keep hair healthy.
- Anti-Humidity Products: Apply anti-humidity products or oils to minimize water absorption and prevent frizz.
- Consult Experts: Seek advice from hair experts or stylists for the best products and practices for your hair type.
Conclusion
Wet hair is much more fragile than dry hair due to the disruption of chemical bonds within the hair structure. It requires gentle handling to prevent damage. Always dry your hair thoroughly before bed and follow a consistent hair care routine to maintain its health and strength.
References
- Popescu, C.; Höcker, H., Hair—the most sophisticated biological composite material. Chemical Society Reviews 2007, 36 (8), 1282-1291. ↩︎
- Wolfram, L. J., Human hair: a unique physicochemical composite. Journal of the American Academy of Dermatology 2003, 48 (6), S106-S114. ↩︎
- Feughelman, M., Natural protein fibers. Journal of Applied Polymer Science 2002, 83 (3), 489-507. ↩︎
- . Feughelman, M., Mechanical hysteresis in wool keratin fibers. Journal of Macromolecular Science, Part B: Physics 1973, 7 (3), 569-582. ↩︎
- Zviak, C., The Science of Hair Care. Taylor & Francis: 1986. ↩︎
- Newman, W.; Cohen, G. L.; Hayes, C., A quantitative characterization of combing force. J. Soc. Cosmet. Chem 1973, 24, 773-782. ↩︎
- KAMATH, Y. K.; HANS-DIETRICH WEIGMANN, Measurement of Combing force. J. Soc. Cosmet. Chem 1986, 37, 111-124. ↩︎
- Wortmann, F. J.; Quadflieg, J. M.; Wortmann, G., Comparing hair tensile testing in the wet and the dry state: Possibilities and limitations for detecting changes of hair properties due to chemical and physical treatments. International Journal of Cosmetic Science 2022, 44 (4), 421-430. ↩︎
