Hello Capilli AI Community,

Welcome to the first edition of the Foundations of Healthy Hair series!

Your hair is more than just a feature of your appearance—it’s a remarkable structure with its own unique anatomy, growth patterns, and care needs.

In this edition, we’ll take a closer look at the structure of hair and uncover the science behind its growth cycle. From understanding the critical components like the cuticle, cortex, and medulla to diving deep into how hair grows and regenerates, this knowledge will empower you to care for your hair like never before.

As we continue this series, we’ll also explore the vital connection between your overall health and the health of your hair. Plus, we’ll show you how advancements in technology, including AI, are transforming personalized hair care.

Hair Anatomy: Beyond the Surface

Hair is far more than what we see on the outside. Its anatomy includes both the visible hair shaft and the hidden follicle, working together to produce and maintain healthy, growing hair. Let’s explore each component in depth:

Hair Shaft

Hair may seem simple at first glance, but it’s composed of intricate layers, each playing a critical role in its strength, flexibility, and health. Hair is made up of three main layers: the cuticle, cortex, and medulla.

Cuticle: The Protective Shield

The cuticle is the outermost layer of the hair shaft, forming a transparent, scale-like barrier that protects the inner layers. It’s made up of overlapping cells, similar to shingles on a roof.

Function

• Shields the cortex from damage caused by environmental stressors (UV rays, pollution) and mechanical wear (brushing, heat styling).

• Regulates moisture by controlling the absorption and release of water.

Structure

• Composed of flattened, keratinized cells that overlap in layers.

• A healthy cuticle lies flat, creating a smooth surface that reflects light, giving hair its shine.

Impact of Damage:

• When the cuticle is lifted or damaged, hair becomes rough, dull, and prone to breakage.

• Harsh chemicals, excessive heat, and overexposure to sunlight can strip the cuticle.

Did You Know?

The cuticle’s overlapping cells are oriented toward the tip of the hair, which is why brushing against the grain (from tip to root) can cause damage.

Cortex: The Core of Strength and Colour

The cortex lies beneath the cuticle and is the thickest layer, accounting for most of the hair shaft’s volume. This layer gives hair its strength, elasticity, and natural pigment.

Function

• Provides mechanical strength and flexibility, allowing hair to bend without breaking.

• Contains melanin granules, which determine hair colour.

Structure

• Made up of long, fibrous keratin proteins arranged in a helical structure.

• Contains two types of melanin:

  1. Eumelanin: Responsible for dark brown and black hair.

  2. Pheomelanin: Responsible for red and yellow tones.

Impact of Damage

• Heat and chemical treatments can break the bonds in the cortex, weakening the hair shaft.

• Loss of melanin with age results in grey or white hair.

Did You Know?

Hair’s ability to stretch up to 30% of its length when wet is thanks to the cortex’s elastic keratin structure.

Medulla: The Mysterious Core

The medulla is the innermost layer of the hair shaft, though it’s not always present. It is primarily found in thicker, coarser hair types.

Function

• Thought to contribute to the hair’s flexibility and thermal insulation, though its exact role is not fully understood.

Structure

• Made of loosely packed, soft keratin and air pockets.

• The medulla is often absent in finer or naturally lighter hair.

Did You Know?

Even though the medulla’s role is less critical, its presence or absence can influence hair’s texture and sheen.

Hair Follicle: The Root of Growth

The hair follicle is a living structure embedded in the dermis of the skin. It’s responsible for producing the hair shaft and supporting its growth. Each follicle operates as a mini-organ, with its own blood supply, nerves, and glands.

Did You Know?

Humans have around 100,000 to 150,000 hair follicles on their scalp alone, and the density of follicles decreases with age.

Key Components of the Hair Follicle

1. Hair Bulb

• Location: The base of the follicle.

• Role: The hair bulb is the growth center of the follicle. It contains rapidly dividing cells called matrix cells, which produce the hair shaft.

• Structure: Surrounds the dermal papilla, which supplies nutrients and growth signals.

• Fun Fact: The shape of the bulb influences hair texture:

  • Round bulbs produce straight hair.

  • Oval bulbs produce wavy hair.

  • Flat bulbs produce curly or coily hair.

2. Dermal Papilla

• Location: At the very base of the hair follicle, nestled within the hair bulb.

• Role: Acts as the follicle’s command center, regulating hair growth through signaling molecules.

• Functionality:

  • Contains capillaries that deliver oxygen and nutrients to the rapidly dividing matrix cells.

  • Produces growth factors, such as VEGF (vascular endothelial growth factor) and IGF-1 (insulin-like growth factor), which are crucial for initiating and maintaining the anagen (growth) phase.

Did You Know?

The size of the dermal papilla correlates with hair thickness. Larger papillae produce thicker hair, while smaller ones lead to finer hair.

3. Inner Root Sheath (IRS)

• Location: Surrounds and protects the growing hair shaft inside the follicle.

• Role: Guides the hair shaft as it grows upward and ensures it maintains its shape.

• Sub-layers:

  1. Cuticle of IRS: Aligns with the hair shaft’s cuticle to lock it in place.

  2. Huxley’s Layer: Acts as a secondary protective layer.

  3. Henle’s Layer: The outermost layer, providing structural support.

4. Outer Root Sheath (ORS)

• Location: Encases the entire follicle and extends from the dermis to the epidermis.

• Role: Protects the follicle and serves as a reservoir of stem cells.

• Stem Cells: These cells in the ORS play a crucial role in hair regeneration and wound healing.

5. Sebaceous Glands

• Location: Attached to the follicle, opening into the upper part of the follicle.

• Role: Produces sebum, a natural oil that:

  • Lubricates the hair shaft.

  • Maintains scalp moisture.

  • Provides antimicrobial protection.

• Overactivity: Leads to oily hair and scalp issues.

• Underactivity: Causes dryness and flakiness.

6. Arrector Pili Muscle

• Location: A tiny muscle connected to the follicle and the dermis.

• Role: Contracts in response to cold or emotional stimuli, causing the hair to stand upright (e.g., goosebumps).

• Evolutionary Function: Goosebumps once helped trap warm air close to the skin in our ancestors or made them appear larger to predators.

7. Follicular Nerves

• Location: Surround the follicle to provide sensory feedback.

• Role: Detect movement of hair shafts, contributing to the sense of touch.

Did You Know?

The follicular nerves are sensitive enough to detect even the slightest movement, such as a breeze brushing through your hair.

The Scalp: A Vital Ecosystem

The scalp provides the foundation for healthy hair growth, acting as a supportive environment for hair follicles.

Components of the Scalp:

• Epidermis: Protects the scalp and houses sebaceous glands.

• Dermis: Contains blood vessels and nerves that nourish and support the follicles.

• Subcutaneous Layer: Cushions the scalp and provides insulation.

Key Scalp Functions:

• Regulates moisture levels through sebum production.

• Supports hair follicles by delivering nutrients and oxygen.

• Protects against environmental damage.

The Hair Growth Cycle: A Closer Look

Hair grows in cycles, and understanding this process is crucial for identifying and addressing hair-related concerns like thinning, shedding, or stunted growth. The growth cycle consists of three main phases:

1. Anagen (Growth Phase)

• Duration: Lasts 2-7 years, depending on genetics, health, and age.

• Activity:

  • The hair follicle is highly active, with cells in the hair bulb dividing rapidly.

  • The dermal papilla plays a critical role by signaling the follicle to produce new hair.

• Percentage of Hair in Anagen: Around 85-90% of scalp hair is in this phase at any given time.

Interesting Fact:

The length of the anagen phase determines how long hair can grow. People with longer anagen phases can grow very long hair, while those with shorter phases cannot.

2. Catagen (Transition Phase)

• Duration: Lasts about 2-3 weeks.

• Activity:

  • Hair growth stops as the follicle detaches from the dermal papilla.

  • The follicle begins to shrink and prepare for the resting phase.

• Percentage of Hair in Catagen: About 1-3% of scalp hair is in this phase.

Did You Know?

This phase marks the end of active growth but is a natural and necessary part of the hair life cycle.

3. Telogen (Resting Phase)

• Duration: Lasts 2-4 months.

• Activity:

  • The hair follicle remains dormant, and the hair shaft is eventually shed.

  • New anagen growth begins beneath the resting hair.

• Percentage of Hair in Telogen: Around 10-15% of scalp hair is in this phase.

Common Concern:

Excessive shedding (telogen effluvium) occurs when a larger-than-usual percentage of hair enters this phase prematurely, often triggered by stress, illness, or hormonal changes.

Additional Phase: Exogen (Shedding Phase)

• Some researchers include an exogen phase as part of the cycle.

• During exogen, the hair shaft is released from the follicle and falls out naturally.

• On average, humans shed 50-100 hairs per day.

Practical Takeaways:

1. Support the Growth Phase:

   • Ensure adequate protein, vitamins (biotin, vitamin D), and minerals (iron, zinc) in your diet.

   • Stimulate blood flow to the scalp with regular massages or tools like scalp massagers.

2. Minimize Stress During Transition and Resting Phases:

   • Manage stress with relaxation techniques to prevent telogen effluvium.

3. Protect Hair During Shedding:

   • Use gentle, sulfate-free shampoos and avoid harsh styling to minimize breakage.

What’s Next?

In the next edition of the Foundations of Healthy Hair series, we’ll explore the essentials of hair health. From hydration and nutrition to environmental protection, you’ll learn how to give your hair the care it needs to thrive.

We’ll also introduce how AI technology is shaping the future of personalized hair care, offering tailored solutions for every hair type and concern.

Thank you for being part of this journey toward healthier, more vibrant hair. We can’t wait to share more with you!

To your health and vitality,
The Capilli AI Team

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Disclaimer:

This newsletter is for informational purposes only and does not substitute professional medical advice. Always consult with a healthcare provider before making any changes to your health regimen.