How much does hair shrink?

Long wet hair that will shrink when drying
Q: I've noticed that my hair always appears longer when it's wet than when it's dry. How much can hair shrink as it dries? Is there a scientific explanation for this shrinking?
A: The scientific explanation for the apparent length difference lies in the unique composition of our hair. Primarily composed of the protein keratin, hair has a porous structure. When it comes into contact with water, it absorbs moisture, causing it to swell. This moisture absorption makes the hair heavier, pulls it down, and creates the temporary extension we observe when it's wet.
As the hair dries, a reverse phenomenon occurs. The previously absorbed water evaporates gradually, leading to a decrease in the hair's moisture content. As this happens, the hair returns to its original, more compact state. The extra weight diminishes, and the hair shrinks. This contraction results in dry hair appearing shorter than when it was wet.
The percentage of hair shrinkage during drying varies from person to person. Factors such as hair porosity, texture (straight, wavy, or curly), and hair health influence the degree of shrinkage. For example, very porous or curly hair may experience more shrinkage compared to less porous or straight hair.
Understanding this dynamic between wet and dry hair is crucial for hairdressers. They need to be well aware of potential shrinkage during the drying phase, as it directly affects the precision of their work. When cutting wet hair, the stylist anticipates the temporary extension due to water absorption, but consideration must also be given to the subsequent shrinkage as the hair dries. The weight of water in wet hair affects not only the apparent length but also how it falls and drapes.
A good understanding of hair shrinkage becomes particularly important when cutting, for example, bangs. The natural shrinkage of hair during the drying process can be the unexpected cause of bangs ending up shorter than originally intended. Therefore, hairdressers must account for this shrinkage when cutting hairstyles with bangs or other precise lengths while the hair is wet.
The hairstyling profession involves a delicate balance between creativity, science, and technical expertise. Experienced hair professionals possess not only the skill to cut a desired style but also the knowledge to understand the complex behavior of hair. By anticipating the natural shrinkage that occurs during the drying process, they ensure that clients leave the salon with a hairstyle that seamlessly aligns with their preferences, free from surprises that can arise from overlooking the dynamics of shrinkage during the drying process.
For a skilled stylist, understanding this interplay between hair and water absorption translates into meticulously planned haircut sessions that consider fluctuations in length during the transition from wet to dry. It is this combination of scientific insight and practical expertise that sets top hairstylists apart from their colleagues.
See also: How to cut hair