When hair becomes wet, it often appears curlier or wavier than its dry state. This transformation involves a fascinating interplay of molecular structures and temporary chemical bonds within the hair. Understanding this phenomenon requires exploring how hair’s fundamental building blocks respond to moisture.
The Fundamental Structure of Hair
Hair is primarily composed of a fibrous protein known as keratin, which provides its strength and shape. Keratin exists as long, coiled molecules. Each hair strand is made up of three layers, with the cortex forming the main bulk and containing these keratin proteins.
The complex structure of keratin in hair is held together by various types of chemical bonds. Three main types are particularly relevant: disulfide bonds, salt bonds, and hydrogen bonds. Disulfide bonds are strong, permanent connections that determine the hair’s natural shape and structural integrity. Salt bonds are temporary and contribute to hair’s strength and elasticity. Hydrogen bonds are the weakest and most flexible, yet they play a crucial role in the hair’s ability to change shape temporarily.
Water’s Interaction with Hair Bonds
Water molecules interact directly with the temporary hydrogen bonds within the hair’s keratin structure. When hair gets wet, water molecules penetrate the hair shaft and disrupt the existing hydrogen bonds that stabilize the hair’s dry shape. This process causes the keratin chains to swell and allows them to shift their positions.
The water molecules then act as bridges, forming new, temporary hydrogen bonds between different points on the keratin protein chains. This rearrangement allows the hair’s protein structure to adopt a more coiled configuration, observed as curling or increased wave definition. This temporary change is why hair can be styled when wet, as water facilitates the rearrangement of these bonds into a new pattern.
Why Hair Types React Differently
The degree to which hair curls when wet is influenced by several inherent characteristics, including its natural curl pattern and porosity. A hair’s natural curl pattern is largely determined by the shape of its follicle; round follicles produce straight hair, while oval or other shaped follicles result in wavy or curly hair. The distribution and number of permanent disulfide bonds also contribute to the hair’s natural curl, with more bonds often leading to curlier hair. These underlying structural differences influence how the keratin proteins are arranged and how they respond to water.
Hair porosity, which refers to the hair’s ability to absorb and retain moisture, also plays a role. It is determined by how open or closed the hair’s outermost layer, the cuticle, is. Hair with high porosity has more open cuticles, allowing water to enter easily and cause significant swelling and curl definition. Conversely, low porosity hair has tightly bound cuticles, making it more resistant to water absorption and less prone to dramatic curling when wet.
What Happens as Hair Dries
As water begins to evaporate from the hair, the temporary hydrogen bonds that formed while the hair was wet become “locked in.” This process stabilizes the hair in its new, curlier or wavier configuration. The reduction of water molecules means the keratin chains can no longer freely shift, and the newly formed hydrogen bonds hold the hair in the shape it dried in.
These water-induced changes are not permanent; the hydrogen bonds are relatively weak and can be easily broken again. Re-wetting the hair, or even exposure to high humidity, can break these bonds, causing the hair to revert to its original dry shape or allow for a new temporary style. This explains why a wet-set curl will disappear with the next wash or in humid conditions, distinguishing it from permanent chemical alterations like perms that affect the stronger disulfide bonds.