The Hair Growth Cycle: Understanding Hair’s Natural Journey

Quick answer: The Hair Growth Cycle is the natural, continuous process each individual hair follicle undergoes, consisting of active growth (anagen), a brief transitional period (catagen), a resting phase (telogen), and shedding (exogen). This cycle ensures hair is regularly renewed, though its duration varies significantly across different body areas and can be influenced by numerous internal and external factors, making it a key aspect of overall hair health and a factor in many hair-related concerns.

Key takeaways

• The Hair Growth Cycle involves distinct anagen (growth), catagen (transition), telogen (rest), and exogen (shedding) phases.
• Each hair follicle cycles independently, meaning not all hairs are in the same phase at once.
• The anagen phase, lasting years for scalp hair, determines hair length, while telogen is a resting phase followed by natural shedding.
• Disruptions to the Hair Growth Cycle are a primary cause of various hair shedding and thinning conditions.
• Factors such as genetics, age, hormones, nutrition, and stress significantly influence the cycle's duration and health.
• Understanding the cycle helps explain common hair changes and informs approaches to maintaining hair and scalp health.

The Hair Growth Cycle: what the evidence shows

The Hair Growth Cycle is a complex biological process that governs the life of each individual hair on the human body, from its initial growth to its eventual shedding and replacement. Far from a synchronised event, every hair follicle operates independently, cycling through distinct stages. This continuous renewal process ensures that hair maintains its protective functions and aesthetic role, consistently replacing older hairs with new ones.

The four distinct phases of hair growth

Scientifically, the hair growth cycle is divided into four main phases: anagen, catagen, telogen, and exogen. Each phase has specific characteristics that dictate the hair's state and activity.

Anagen (Growth Phase)

Anagen is the active growth phase, during which hair cells rapidly divide in the hair bulb, forming new hair fibre. This is the longest phase of the cycle. For scalp hair, anagen typically lasts for 2 to 7 years, though genetic factors, age, and overall health can cause significant individual variation. The duration of this phase is crucial, as it largely determines the maximum length a hair can achieve. At any given time, approximately 85% to 90% of all scalp hairs are in the anagen phase.

During anagen, the hair follicle is deeply anchored in the dermal layer of the skin, receiving essential nutrients and oxygen from the dermal papilla, a structure rich in capillaries. This nourishment supports the active growth of the hair shaft as it emerges from the skin and lengthens.

Catagen (Transition Phase)

Following the anagen phase, the hair follicle enters catagen, a short transitional period that signals the end of active growth. This phase typically lasts for 2 to 3 weeks, and only about 1% to 2% of scalp hairs are in catagen at any moment. During catagen, active hair growth ceases, and the hair follicle begins to shrink. The lower part of the follicle regresses and detaches from the dermal papilla. The hair bulb shrivels, and the hair shaft transforms into a "club hair", preparing for its eventual release.

Telogen (Resting Phase)

Telogen is the resting phase of the Hair Growth Cycle, typically lasting about 3 to 4 months. Approximately 10% to 15% of scalp hairs are in this phase at any given time. During telogen, the hair follicle is completely inactive, and no new growth occurs. The club hair remains within the follicle, though it is no longer actively attached to the dermal papilla. Towards the end of the telogen phase, a new anagen hair often begins to grow beneath the resting hair, gently pushing it out. This mechanism facilitates natural hair replacement.

Exogen (Shedding Phase)

Exogen is the active shedding phase, which is sometimes considered part of the telogen phase but is increasingly recognised as distinct. This phase specifically refers to the natural release of the old club hair from the follicle. While it often coincides with the onset of a new anagen hair pushing the old one out, shedding can also occur independently. It is entirely normal to shed between 50 to 100 hairs per day as part of this natural process, ensuring a continuous turnover of hair.

The mechanism behind the Hair Growth Cycle

The intricate timing and progression of the Hair Growth Cycle are regulated by a complex interplay of genetic programming, hormones, growth factors, and signalling molecules within the hair follicle. The dermal papilla plays a crucial role, acting as a signalling centre that communicates with the surrounding follicular cells to orchestrate the transition between phases. Stem cells within the hair follicle also contribute significantly to the regeneration of new hair in each cycle.

Factors influencing the Hair Growth Cycle

The duration and regularity of the Hair Growth Cycle are not fixed and can be influenced by a wide array of internal and external factors. Understanding these influences is key to understanding changes in hair health.

• Genetics: Individual genetic predispositions are a primary determinant of the anagen phase's length and overall hair density. Genetic factors can also predispose individuals to certain hair loss conditions.
• Age: As individuals age, the anagen phase may progressively shorten, leading to a higher proportion of hairs entering the telogen phase. This can result in overall thinner-looking hair and reduced hair density over time.
• Hormonal Changes: Hormones have a profound impact on hair growth. For example, androgens can miniaturise hair follicles in genetically predisposed individuals, contributing to conditions like androgenetic alopecia. Significant hormonal shifts, such as those during pregnancy or menopause, can dramatically affect the cycle. Pregnancy often extends the anagen phase, leading to thicker hair, followed by increased shedding (telogen effluvium) postpartum as hair follicles reset.
• Nutrition: A balanced diet rich in essential vitamins (such as biotin and vitamin D), minerals (like iron and zinc), and proteins is vital for healthy hair growth. Deficiencies in these nutrients can prematurely shorten the anagen phase and trigger increased shedding. For instance, iron deficiency is a known cause of telogen effluvium.
• Stress: Both physical and psychological stress can profoundly impact the Hair Growth Cycle. Chronic or severe stress can prematurely shift a significant number of hair follicles from the active anagen phase into the resting telogen phase, leading to a widespread increase in hair shedding known as telogen effluvium, often occurring 2 to 3 months after the stressful event.
• Medical Conditions and Medications: Various medical conditions, including thyroid disorders, autoimmune diseases, and scalp infections, can disrupt the Hair Growth Cycle. Certain medications, such as chemotherapy drugs, blood thinners, and some antidepressants, can also interfere with the cycle, causing hair shedding or changes in hair texture. For example, chemotherapy often induces anagen effluvium, where hair is shed rapidly during the growth phase.
• Hair Care Practices: Harsh chemical treatments, excessive heat styling, tight hairstyles, and aggressive brushing can cause hair breakage, which should not be confused with changes in the Hair Growth Cycle or hair shedding. While these practices do not alter the cycle itself, they can lead to noticeable hair loss in terms of fibre length and density. Refer to "Hair Damage: Causes, Signs, and Solutions" for more information.

The Hair Growth Cycle and hair shedding

Disruptions to the normal Hair Growth Cycle are the underlying cause of various forms of hair shedding and thinning. It's important to distinguish between typical daily shedding and excessive hair loss. Understanding which part of the cycle is affected is crucial for proper diagnosis and management.

• Androgenetic Alopecia (Pattern Hair Loss): This common condition is characterised by a progressive shortening of the anagen phase and the miniaturisation of hair follicles, leading to the growth of finer, shorter, and less pigmented hairs over time. This process eventually leads to noticeable thinning and pattern hair loss.
• Telogen Effluvium: This condition occurs when a sudden or significant stressor (such as illness, surgery, childbirth, severe emotional stress, or nutritional deficiencies) causes a large number of hairs to prematurely enter the telogen (resting) phase. This results in widespread hair shedding typically 2 to 3 months after the triggering event, as these hairs are subsequently released. Once the stressor is removed, the Hair Growth Cycle usually normalises.
• Anagen Effluvium: This rapid and extensive hair shedding occurs during the anagen phase, often caused by agents that interfere with cell division, such as chemotherapy, radiation therapy, or exposure to certain toxins. Hair is shed directly from the growing phase, leading to sudden and significant hair loss.

Hair Cycle duration comparison

The duration of the Hair Growth Cycle varies significantly depending on the body area, illustrating the body's tailored approach to hair length and density in different regions.

Body Area	Anagen Phase	Catagen Phase	Telogen Phase
Scalp Hair	2 to 7 years	2 to 3 weeks	3 to 4 months
Eyebrows	1 to 3 months	2 to 3 weeks	1 to 2 months
Eyelashes	1 to 2 months	2 to 3 weeks	1 to 2 months
Body Hair	1 to 6 months	2 to 3 weeks	3 to 6 months

When to get professional advice

While some daily hair shedding is normal, it's advisable to consult a general practitioner or a dermatologist if you notice any significant or sudden changes in your hair density, an increase in shedding beyond the typical 50 to 100 hairs per day, or the appearance of bald patches. Early diagnosis of any underlying conditions affecting the Hair Growth Cycle can lead to more effective management.

Frequently asked questions about the Hair Growth Cycle

Can diet impact the Hair Growth Cycle?

Yes, diet plays a crucial role. A diet lacking essential nutrients such as iron, zinc, biotin, and vitamins A, C, D, and E can disrupt the normal Hair Growth Cycle. These deficiencies can shorten the anagen phase and lead to increased shedding (telogen effluvium). Ensuring a balanced intake of these nutrients supports healthy hair growth and overall cycle regulation.

Does stress really cause hair to shed more?

Yes, stress is a significant factor. Both severe emotional stress and physical stressors (like illness or surgery) can push a large number of hair follicles prematurely into the telogen (resting) phase. This can result in noticeable hair shedding, typically 2 to 3 months after the stressful event. Managing stress can help restore a healthy Hair Growth Cycle.

How long does it take for hair to grow back after shedding?

After a hair sheds from the telogen or exogen phase, the follicle enters a new anagen phase to begin growing a new hair. This process typically takes a few weeks to a few months for the new hair to become visible above the scalp. The full regrowth to a noticeable length will depend on the length of the anagen phase for that specific hair, which can take years for scalp hair.

Can hair products alter the Hair Growth Cycle?

Topical hair products primarily affect the hair shaft and scalp health, rather than directly altering the internal Hair Growth Cycle within the follicle. However, a healthy scalp environment, supported by suitable products, can indirectly support optimal follicular function. Harsh products or those causing irritation could potentially contribute to scalp issues that might influence shedding patterns, but they don't change the fundamental phases of the cycle.

Is it normal to shed hair every day?

Yes, it is entirely normal to shed between 50 to 100 hairs each day as part of the natural Hair Growth Cycle. This shedding is primarily from the exogen phase, where old hairs are released to make way for new growth. This daily turnover ensures that your hair remains healthy and renewed.

Supporting your Hair Growth Cycle with Watermans

Maintaining a healthy Hair Growth Cycle involves a holistic approach, including good nutrition, stress management, and appropriate hair care. Watermans products are formulated with ingredients that aim to support optimal hair and scalp health, creating an environment conducive to healthy-looking hair. Ingredients such as biotin, often associated with hair health, and zinc, an essential mineral, are found in Watermans formulations. While no cosmetic product can fundamentally alter the biological Hair Growth Cycle, supporting scalp health and providing beneficial nutrients to the hair fibre can contribute to stronger-feeling hair and a healthier-looking scalp, helping to reduce the appearance of breakage and support fuller-looking hair.

Sources and references

• American Academy of Dermatology Association, "Hair Loss: Diagnosis and Treatment"
• British Association of Dermatologists, "Hair Loss Information"
• Journal of Clinical and Aesthetic Dermatology, "Hair Biology: An Update"
• National Institute of Health (NIH), "Hair Growth"
• PubMed, Various articles on hair follicle biology and hair growth disorders
• NHS, "Hair loss"
• University of California San Francisco, Department of Dermatology, "The Hair Follicle"
• The Skin Cancer Foundation, "The Hair Growth Cycle: What It Is and How It Works"

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Find these ingredients in Watermans products

• Biotin: you will find this ingredient in our Hair Growth Shampoo.
• Zinc: you will find this ingredient in our Hair Vitamins.