Hair shrinkage is a common experience for those with textured hair. It is the temporary reduction in the visible length of the hair strand, sometimes reaching 75% of the hair’s actual length when fully stretched. Shrinkage is a physical phenomenon that occurs when the hair dries after being saturated with water.
The Science Behind Hair Shrinkage
Shrinkage is a direct consequence of the hair’s internal structure and its interaction with water molecules. The hair shaft is primarily made up of keratin protein, forming a dense inner layer called the cortex, which is wrapped in a protective outer layer, the cuticle. The cortex is where the temporary hydrogen bonds reside.
When textured hair absorbs water, the hydrogen bonds temporarily break down. This allows the keratin proteins in the cortex to swell and the hair strand to elongate. As the water evaporates during the drying process, the hydrogen bonds reform, but they reset in a tightly coiled, contracted configuration dictated by the natural curl pattern of the hair shaft. This recoiling is the physical action of shrinkage.
Defining the Duration of the Shrunken State
The initial shrinking process, where the hair transitions from wet to its fully coiled dry state, happens quickly as water leaves the strand. This process is generally complete once the hair is entirely dry, typically within a few hours depending on density and environment.
The shrunken state itself is indefinite, lasting as long as the environment and styling methods remain unchanged. The hair will stay in its coiled, shrunk configuration until the existing hydrogen bonds are broken and reformed into an elongated shape. This requires either the reintroduction of water or moisture, which breaks the bonds, or a physical manipulation technique that stretches the bonds while they set.
Environmental and Styling Factors That Maintain Shrinkage
The presence of moisture in the surrounding air maintains the hair’s shrunken state. High humidity, defined as a moisture level above 40%, introduces water vapor into the air, which the hair readily absorbs. This constant absorption prevents the hair’s internal hydrogen bonds from fully settling into an elongated style, causing them to revert to the natural, tightly coiled form.
Air-drying without any physical manipulation also contributes to maintaining the shrunken state, as the hair is left free to recoil naturally as it dries. Furthermore, hair porosity, or the ability of the hair to absorb and retain water, influences the duration of shrinkage. High-porosity hair, with its raised cuticle layer, can absorb and lose moisture quickly, leading to rapid and often more pronounced shrinkage whenever exposed to environmental moisture. Product choices can also play a role; water-based curl-defining creams and gels encourage the initial coiling action, thereby setting the hair in a shorter, shrunken style.
Methods for Length Retention and Stretching
Styling techniques must physically manipulate the hair to hold an elongated shape while the hydrogen bonds reset. Low-tension methods are used to stretch the hair as it dries. These methods include techniques like banding, where elastic ties are placed along the length of a section of hair to keep it stretched as it dries, and African threading, which uses thread wrapped around the hair.
Protective styles such as braid-outs and twist-outs physically elongate the hair by forcing the curl pattern into a looser wave or coil. The hair is set in these styles while damp, and the physical tension holds the keratin proteins in a stretched position as the hydrogen bonds reform.
Low-heat methods, like tension blow-drying, use a low-temperature airflow with a nozzle to gently pull the hair straight while drying. This heat-assisted process helps set the hydrogen bonds in a straightened configuration, but a heat protectant should always be applied first to shield the hair’s protein structure from potential damage.