Hair

What Exactly is Hair?

Hair, a protein filament that grows from follicles found in the dermis, is one of the defining characteristics of mammals. But have you ever wondered about its structure and function? Let’s dive into the fascinating world of hair.

The Structure of Hair

Each strand of hair consists of three layers: the medulla, cortex, and cuticle. The cortex, which contains melanin, colors the fiber based on its distribution and types of granules. The diameter of human hair varies from 0.017 to 0.18 millimeters, making it a crucial component in our daily lives.

Types of Hair

The word ‘hair’ is derived from Middle English and Old Norse words, with influences from other Germanic languages such as Swedish, Dutch, and German. Some characteristics in human head hair vary by race: African ancestry has a hair diameter of 60–90 μm and flat cross-section; European or Middle Eastern ancestry has a hair diameter of 70–100 μm and oval cross-section; Asian or Native American ancestry has a hair diameter of 90–120 μm and round cross-section. These variations play a significant role in the texture, volume, and consistency of our hair.

Functions of Hair

Hair serves multiple functions, including thermal regulation, camouflage, signaling, and sensory input. The root contains fibrous connective tissue, glassy membrane, external and internal root sheath, cuticle, cortex, and medulla. These components work together to ensure the proper growth and maintenance of hair.

Hair Growth

Hair growth begins inside the hair follicle, with only living cells found in the follicle and dead shaft. The three stages of hair growth are anagen (growth phase), catagen (regression phase), and telogen (resting phase). The root contains fibrous connective tissue, glassy membrane, external and internal root sheath, cuticle, cortex, and medulla. Caucasian hair growth rate: previously thought to be faster than Asian hair, but research shows no significant difference between men and women.

Texture of Hair

The texture of human hair varies in curl pattern, volume, and consistency. Curl patterns are determined by the shape of the hair shaft; volume is determined by the size of the follicle; and consistency is grouped into fine, medium, and coarse categories. Various classification systems exist to classify curl patterns, including the Andre Walker system.

Evolutionary Significance

Hair has its origins in the common ancestor of mammals, the synapsids, about 300 million years ago. The oldest undisputed known fossils showing unambiguous imprints of hair are the Callovian (late middle Jurassic) Castorocauda and several contemporary haramiyidans, both near-mammal cynodonts. Hair composition consists mainly of keratin proteins and KRTAPs, which encode for various amounts of keratins in different amounts.

Social Significance

Hair has social significance and can be used to indicate status, age, health, ethnicity, and group membership. The length and style of hair can convey messages about an individual’s identity, status, and affiliation with a particular group or culture. Many people have worn long hair for various reasons and cultures, including hippies, metalheads, Indian sadhus, and older hipsters.

Global Imports of Hair

The global imports of hair were worth $1.24 billion in 2010. This industry includes the removal practices such as shaving, waxing, and depilation. Shaving is accomplished using bladed instruments, while epilation removes the entire hair strand through methods like waxing.

Conclusion

Hair is more than just a physical feature; it’s a complex structure with multiple functions that have evolved over millions of years. From its origins in ancient mammals to its current social and cultural significance, hair continues to play an important role in our lives.