Hair structure and differences in human body hair: Features of eyelash and eyebrow hairs.

Introduction

Hair plays an important role not only aesthetically but also functionally. Understanding hair structure and the differences between various types of body hair is essential for lamimakers, brow artists, and lashmakers. Hair on different body parts has unique characteristics that influence the care methods and products used. In this article, we’ll explore the main types of hair, its structure, and the renewal cycles of hair strands.

Human Hair Structure: Everything You Need to Know

Human hair is a significant part of our appearance and health. Hair covers 95% of the human skin surface, serving various functions, from protection to thermoregulation.

There are three main types of hair on the human body:

1. Long hair — covers the scalp, underarms, and pubic area, while in men, it includes the beard and mustache. Long hair has a distinct medulla and thick cortex, which provide strength and flexibility. The follicles of long hair are deep in the skin, with a life cycle lasting several years.

2. Bristly hair — shorter hair located on eyebrows, eyelashes, and in the nasal and ear areas. It has a dense cortex and little or no medulla. Bristly hair provides protection for specific areas and generally does not serve a thermoregulatory function. It renews more quickly than long hair and is more rigid, requiring special care when performing hair removal procedures.

3. Vellus hair — thin and nearly invisible hair covering most of the body, providing slight protection and insulation. Vellus hair usually lacks a medulla and has a very thin cortex.

The term "terminal hair" usually refers to long hair, however, some experts combine long and bristly hair into one group, and call it "terminal-bristly hair"

The term "vellus hair" refers to vellus hair.

Basic Hair Structure

Let’s explore hair structure in detail. First, each hair consists of two main parts: the root and the shaft. Each of these has unique features and functions, ensuring hair growth, strength, and health.

1. Root and Shaft

Shaft — the part of the hair above the skin's surface. It consists of three layers: the cuticle, cortex, and medulla. The shaft determines the hair’s appearance, texture, strength, and color. Not all hair types have all three layers — refer to the article above for details.

Root — the part below the skin, within the hair follicle. The root holds the hair in place and provides its nourishment.

2. Structure of the Hair Shaft in Cross-Section

The hair shaft consists of three layers:

1. Cuticle — the outer layer made of thin flat cells arranged in semi-circular scales, like roof tiles. The cuticle provides protection for the inner layers from mechanical damage and moisture loss.

2. Cortex — the middle and thickest layer, making up the main part of the shaft. It consists of keratin fibers that give hair strength, elasticity, and color. The cortex is responsible for hair's physical properties, like flexibility and strength.

3. Medulla — the central layer. In fine hair, particularly in eyelashes and eyebrows, the medulla may be absent or less pronounced. It consists of cells filled with air or fluid, which can affect the hair’s insulation properties.

3. Root Structure, Bulb, and Follicle

The terms “hair root,” “hair follicle,” and “hair bulb” are often used interchangeably, but they are not the same. Some hair structure researchers differentiate between the root (part of the hair below the skin), the bulb (lower part of the root), and the follicle (the sac in which the bulb is located). It is within the bulb where all processes related to hair growth take place. The bulb contains Langerhans cells, Merkel sensory cells, and melanocytes, along with cells similar to the basal and spinous layers of the epidermis.

• Hair papilla — the central part of the bulb, responsible for nourishing the hair. Through the papilla, nutrients from blood vessels are delivered to the hair.

• Hair bulb — the part of the root where active cell division occurs. The bulb supports new hair growth and determines its structure.

• Hair follicle sheaths — inner (ORS) and outer (IRS) sheaths that support and protect the hair. They also play a crucial role in hair growth and regeneration.

An interesting fact about follicle shape — a rounded follicle produces straight hair, an oval follicle produces wavy hair, and a kidney-shaped follicle produces curly hair.

Differences in the Structure of Eyelashes and Eyebrows

Eyelashes and eyebrows are types of bristly hair, and unlike long hair, they lack an arrector pili muscle. However, they have some specific characteristics:

• Eyelashes — short, sturdy hairs made of two or three layers. They serve a protective function, preventing dust and particles from entering the eyes. The eyelash growth cycle is much shorter, making them vulnerable to external influences.

• Eyebrows — also short hairs, giving expressiveness to the face and protecting the eyes from sweat and rain. Eyebrow hairs renew approximately every 4-6 months, making procedures such as eyebrow tinting and eyelash lamination particularly relevant to maintain their appearance.

In upcoming articles, we will also discuss skin layers, the chemical structure of hair, growth stages, and cellular structure.

Conclusion

These structural features make hair a complex yet perfect system that not only adds beauty but also performs essential functions for the human body.

Understanding hair structure and its life cycle, particularly of eyelashes and eyebrows, is essential for professionals involved in brow tinting, eyelash extension, and lamination. Knowing the layers, structure, and functions of hair helps in choosing the most suitable products and care methods. Proper techniques and tools will ensure lasting results and protect hair from damage.

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