What Is Hair Structure and How Does It Grow? | Jae Pak MD

- Reviewed by: Dr. Jae Pak, M.D.

What Is Hair Structure and How Does It Grow?

Hair, a defining feature of mammals, plays a crucial role in our biological functioning and in shaping human aesthetics and identity. Beyond its visual appeal, hair serves as a protective barrier and indicates individual health. 

Understanding the complexities of hair structure and the intricacies of its growth process is not only fascinating but also essential for maintaining healthy hair. 

This article explores the details of hair structure and the growth cycle and uncovers the factors affecting hair health and growth. By the end of this journey, readers will gain a comprehensive insight into why hair behaves the way it does and how to nurture it effectively.

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What Is the Structure of Your Hair?

Our hair is made up of many parts. This includes:

The Hair Shaft

The hair we see and style every day is known as the hair shaft or our hair strands. This visible part of the hair is intricately structured, primarily consisting of three layers: the cuticle, cortex, and, in some cases, the medulla.

  • Cuticle: The outermost layer, the cuticle, comprises overlapping scales that protect the inner layers of the hair. These scales determine the hair’s shine and smoothness and prevent hair damage and breakage.
  • Cortex: Beneath the cuticle lies the cortex, which contains fibrous proteins and pigments that give hair its hair color and texture. The strength, elasticity, and moisture of the hair largely depend on the health of the cortex.
  • Medulla: The innermost layer, present in some hair types, is the medulla. This layer is not always present, and its function is not fully understood, but it’s believed to contribute to the hair’s strength and stability.

The hair shaft primarily comprises keratin, a strong protein that also forms nails and the outer layer of skin. This protein structure is what gives hair its remarkable resilience and ability to withstand various stresses.

The Hair Follicle

The journey of each hair begins in the hair follicle, a tiny but complex structure beneath the epidermis (skin’s surface). The follicle is where hair is produced, and understanding its structure is key to comprehending hair growth and health.

  • Anatomy of the Follicle: Each follicle is a tube-like pocket in the skin, extending to the dermis. It houses the hair root, where cells divide to build the hair shaft.
  • Role in Hair Growth: The base of the follicle is the hair bulb, containing active cells that grow and build the hair shaft. Blood vessels in the follicle provide the nutrients necessary for these cells, and hormones influence their activity, affecting hair growth and structure.

The hair shaft and follicle work in tandem, creating and nurturing the hair we see. Their health and functionality are vital for maintaining the hair’s appearance and overall condition.

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What Is the Hair Growth Cycle?

Understanding the hair growth cycle is essential for comprehending how hair grows and why it sometimes doesn’t. 

This cycle is a continuous process and can be divided into three distinct phases:

Anagen (Growth Phase)

This is the active phase of hair growth, during which the cells in the root of the hair are dividing rapidly. A new hair is formed and pushes the club hair (a hair that has stopped growing) up the follicle and eventually out. The anagen phase can last from two to six years and determines the length of our hair.

Catagen (Transition Phase)

Following the anagen phase, the hair enters the catagen phase, which lasts about two to three weeks. In this phase, the hair follicle shrinks and detaches from the dermal papilla, a structure critical for hair growth.

Telogen (Resting Phase)

The final phase is the telogen phase, lasting around three months. During this time, the hair is at rest, and no active growth occurs. At the end of the telogen phase, the hair follicles re-enter the anagen phase, new hair begins to grow, and the old hair is shed.

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What Are the Factors Influencing the Growth Cycle?

Several factors can influence the hair growth cycle, including:

  • Genetics: Genetics plays a significant role in determining hair growth, thickness, and density.
  • Age: As people age, the rate of hair growth can slow down, and the hair may thin or lose its pigment.
  • Hormonal Influences: Hormones significantly impact hair growth. Changes in hormonal levels due to pregnancy, menopause, or endocrine disorders can affect the hair growth cycle.

What Is the Nutritional and Environmental Impact on Hair Health?

Just like any other part of the body, hair health is significantly influenced by nutrition and environmental factors.

Nutritional Factors

Nutrients play a crucial role in maintaining healthy hair. It also helps reduce scarring when recovering from hair transplant surgery. Lack of certain vitamins and minerals can lead to hair loss or slow hair growth. 

Essential nutrients for hair health include:

  • Protein: Hair is primarily made of protein, so adequate protein intake is crucial.
  • Iron: Iron deficiency is a common cause of hair loss, especially in women.
  • Vitamins: Vitamins A, C, D, and E, along with the B vitamins, particularly biotin, are vital for hair health.
  • Omega-3 Fatty Acids: These fats are important for hair growth and overall scalp health.

Environmental Factors

The environment can also impact hair health in various ways:

  • Pollution: Pollutants can damage the hair and scalp, leading to hair loss and dullness.
  • Climate: Extreme weather conditions, like excessive sun or cold, can stress the hair.
  • Chemical Treatments: Frequent use of harsh chemicals in hair treatments can weaken the hair and damage the scalp.

Understanding these factors is crucial for maintaining healthy hair. The next section will explore common hair concerns and how to address them.

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What Are Common Hair Concerns and Disorders?

Hair issues can be distressing, affecting not just appearance but also self-esteem. Understanding common hair concerns and disorders is the first step toward effective management and treatment.

Hair Loss and Thinning

Hair loss can be attributed to various factors, including genetic predisposition (as in male or female pattern baldness), stress, hormonal changes, nutritional deficiencies, and certain medical conditions.

  • Alopecia Areata: An autoimmune disorder causing patchy hair loss.
  • Androgenetic Alopecia: Known as male or female pattern baldness, this is characterized by a gradual thinning of hair.
  • Telogen Effluvium: A temporary condition often triggered by stress, illness, or hormonal changes, resulting in diffuse hair shedding.

Treatments vary depending on the cause and may include topical treatments like minoxidil, oral medications, lifestyle changes, or, in some cases, surgical options like hair transplantation.

Other Hair Disorders

  • Dandruff: Caused by an overgrowth of scalp fungus or excessive oil production (sebum) from our sebaceous glands, leading to flaking and itching. Treatment typically involves using anti-dandruff shampoos containing zinc pyrithione or ketoconazole.
  • Split Ends and Brittleness: Often a result of mechanical stress, heat styling, and lack of moisture. Regular trimming, gentle handling, and deep conditioning treatments can help manage these issues.
  • Scalp Conditions: Various scalp conditions like psoriasis or seborrheic dermatitis can affect hair health. Treatment may require medicated shampoos or prescription medications.

Lasting Hair Health: Your Path to Vibrant Locks

Remember, your hair’s health is a reflection of your lifestyle, environment, and the care you provide. Knowing the structure and growth cycle of hair is more than just a scientific curiosity; it’s a pathway to achieving and maintaining the health and beauty of your locks.

For those who have been diagnosed with hair loss by a primary care provider or dermatologist, experts like Dr. Jae Pak can offer invaluable assistance. As a specialist in hair transplants and Scalp MicroPigmentation, Dr. Pak uses his deep understanding of hair biology and the latest advancements in hair restoration to provide tailored solutions to meet your needs.  

Whether you’re dealing with diagnosed hair loss or exploring restoration options, working with Dr. Pak can be a significant step in your hair restoration journey.


The Diagnosis and Treatment of Hair and Scalp Diseases | NIH

Losing Hair From Stress? What You Should Know About Hair Loss and Chronic Stress | UPMC Health Beat

Diet and hair loss: effects of nutrient deficiency and supplement use | NIH

What is the structure of hair and how does it grow? | NIH

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