The Hair Growth Cycle: Understanding Hair Growth and Renewal

Quick answer: The Hair Growth Cycle is the continuous process by which hair follicles produce and renew hair strands, consisting of four distinct phases: anagen (active growth), catagen (transition), telogen (resting), and exogen (shedding). Each hair follicle operates independently, meaning different hairs are in different stages at any given time, preventing simultaneous mass shedding. Understanding this cycle helps explain natural hair renewal and differentiate it from excessive hair shedding or hair loss. However, the exact duration of each phase can vary significantly between individuals and across different body regions, and is influenced by many factors.

Key takeaways

• Hair growth is a dynamic, cyclical process orchestrated by hair follicles, renewing hair strands throughout life.
• The Hair Growth Cycle consists of four main phases: anagen (active growth), catagen (short transition), telogen (resting), and exogen (shedding).
• Approximately 85% to 90% of scalp hairs are in the anagen phase at any given time, which can last from 2 to 7 years.
• Normal daily hair shedding, typically 50 to 100 hairs, is a natural part of the exogen phase and indicates healthy renewal.
• Many factors, including genetics, age, hormones, nutrition, and stress, can influence the duration and health of each phase.
• Disruptions to the cycle can lead to increased hair shedding (like telogen effluvium) or hair loss (where new growth is impaired or follicles miniaturise).

The Hair Growth Cycle: What the evidence shows

Hair growth is not a continuous, steady process, but rather occurs in a precise, repeating sequence known as The Hair Growth Cycle. This cycle ensures that hair follicles, the tiny organs in your skin responsible for growing hair, continuously produce and renew hair strands. Each hair follicle on your head operates independently, meaning different hairs are always in different phases of the cycle. This asynchronous activity is why you don't lose all your hair at once, but rather experience a constant, subtle shedding of older hairs as new ones emerge.

Understanding these phases is fundamental to distinguishing normal hair renewal from excessive hair shedding or genuine hair loss. While the exact duration of each phase can vary significantly between individuals, hair location on the body, and genetic factors, the sequence remains consistent.

The four distinct phases of the hair growth cycle

The Hair Growth Cycle is typically described in four main phases: Anagen, Catagen, Telogen, and Exogen. Each phase has specific biological functions that contribute to the overall process of hair renewal.

1. Anagen (Growth Phase)

The anagen phase is the active growth period. During this time, cells within the hair bulb (the base of the hair follicle) divide rapidly. These new cells push upwards, forming the hair shaft and causing the hair to lengthen. The anagen phase is the longest phase, typically lasting between 2 and 7 years for scalp hair, though it can be shorter for hair on other parts of the body. The duration of this phase is primarily genetically determined and dictates the maximum length your hair can naturally achieve. At any given moment, about 85% to 90% of the hairs on a healthy human scalp are in the anagen phase.

2. Catagen (Transition Phase)

Following the anagen phase, the hair follicle enters a short transitional period called catagen. This phase lasts only about 2 to 3 weeks. During catagen, the hair follicle begins to shrink, detaching itself from its blood supply in the dermal papilla, which nourishes the hair. Hair growth ceases, and the hair forms a "club hair" at its base, preparing for the resting phase. Only around 1% of scalp hairs are in the catagen phase at any one time.

3. Telogen (Resting Phase)

The telogen phase is a resting period for the hair follicle, lasting approximately 2 to 4 months for scalp hair. The club hair remains in the follicle but is no longer actively growing. The follicle itself enters a dormant state, awaiting the signal to restart the anagen phase. Around 10% to 15% of scalp hairs are typically in the telogen phase. Towards the end of this phase, a new anagen hair often begins to grow beneath the existing club hair, gently pushing it out.

4. Exogen (Shedding Phase)

Although sometimes considered part of the telogen phase, exogen is increasingly recognised as a distinct shedding phase. This is when the old club hair is released from the follicle and falls out. This shedding is a normal and necessary part of the hair renewal process, making way for the new hair to emerge. It's perfectly normal to lose between 50 and 100 hairs per day as part of this natural cycle. Shedding beyond this amount, or shedding accompanied by thinner new growth, can indicate a disruption to the cycle.

Factors influencing the hair growth cycle

Many factors can influence the duration and health of each phase of The Hair Growth Cycle, thereby affecting overall hair density, texture, and growth patterns. These influences can lead to variations in hair health and appearance.

Genetics

Your genetic makeup plays the most significant role in determining the length of your anagen phase, the overall density of your hair, and even your predisposition to certain types of hair thinning or loss. For example, some people are genetically inclined to have a longer anagen phase, allowing their hair to grow much longer.

Age

As you age, the hair growth cycle can naturally change. The anagen phase may shorten, and hair follicles can produce finer, thinner hair. This can lead to a gradual decrease in overall hair volume and density, often observed in both men and women as they get older.

Hormonal changes

Hormones have a profound impact on the hair growth cycle. Fluctuations due to pregnancy, childbirth, menopause, or conditions affecting the thyroid gland can alter the cycle. For instance, increased oestrogen during pregnancy can prolong the anagen phase, leading to thicker, fuller-feeling hair. Conversely, the sudden drop in oestrogen after childbirth can trigger a mass synchronisation of follicles into the telogen phase, resulting in a temporary increase in hair shedding known as telogen effluvium.

Nutrition

A balanced diet rich in essential vitamins, minerals, and proteins is crucial for healthy hair growth. Deficiencies in nutrients like iron, zinc, biotin, and vitamins D and C can disrupt the normal hair growth cycle, potentially leading to weakened hair fibres, increased breakage, or excessive shedding. For more on essential nutrients, see 'Lupin Protein: Benefits, Mechanisms, and Haircare Applications'.

Stress

Both physical and emotional stress can significantly impact the hair growth cycle. Chronic or severe stress can prematurely shift a larger number of hair follicles from the anagen (growth) phase into the telogen (resting) phase. This often results in noticeable hair shedding approximately 2 to 3 months after the stressful event, a condition known as telogen effluvium.

Medical conditions and medications

Certain medical conditions, such as autoimmune diseases, scalp infections, and thyroid disorders, can interfere with The Hair Growth Cycle. Similarly, some medications, including certain chemotherapy drugs, blood thinners, and antidepressants, can cause alterations to the cycle, leading to increased shedding or hair loss. Always discuss any concerns about medication side effects with your doctor.

Normal shedding versus hair loss

Understanding The Hair Growth Cycle is key to differentiating normal hair shedding from genuine hair loss. Normal shedding is part of the exogen phase, where old hairs are released to make way for new growth, typically 50 to 100 hairs per day. This is a natural and healthy process.

Hair loss, however, refers to a situation where the rate of shedding significantly exceeds the rate of new growth, or when the new hair produced is progressively weaker, miniaturised, or fails to grow at all. It's important to distinguish between hair shedding (hair leaving the follicle) and hair breakage (the hair fibre snapping along the shaft). Hair breakage can make hair appear thinner or shorter but does not indicate a problem with the hair follicle itself. See 'Hair Damage: Causes, Signs, and Solutions' for more information.

For example, in androgenetic alopecia (pattern hair loss), the anagen phase progressively shortens, and hair follicles miniaturise over time, producing finer, shorter, and fewer hairs with each cycle. Conditions like chronic telogen effluvium involve persistent, increased shedding where many follicles enter the telogen phase simultaneously without sufficient new growth. If you are experiencing persistent or noticeable hair changes, professional advice is recommended.

When to get professional advice

If you are experiencing significant or sudden changes in your hair, such as increased shedding beyond the normal 50 to 100 hairs per day, patches of hair not growing back, or noticeable thinning, it is advisable to seek professional medical advice. A dermatologist or trichologist can accurately diagnose the cause of any hair changes and recommend appropriate management or treatment. Early diagnosis can be important for conditions that affect The Hair Growth Cycle.

Frequently asked questions about The Hair Growth Cycle

How many hairs do we lose daily during The Hair Growth Cycle?

It's completely normal to lose between 50 and 100 hairs each day as part of the exogen (shedding) phase of The Hair Growth Cycle. This is a natural part of hair renewal, making way for new hair growth. If you notice significantly more hair shedding than this, especially over a prolonged period, it might indicate a disruption to the cycle.

Can stress really affect The Hair Growth Cycle?

Yes, stress can significantly impact The Hair Growth Cycle. Both acute and chronic stress can prematurely push a larger number of hair follicles into the telogen (resting) phase. This typically results in increased hair shedding, known as telogen effluvium, which often becomes noticeable about 2 to 3 months after the stressful event. Managing stress can help support a healthy cycle.

How long does each phase of The Hair Growth Cycle last?

The anagen (growth) phase usually lasts 2 to 7 years for scalp hair. The catagen (transition) phase is brief, lasting only 2 to 3 weeks. The telogen (resting) phase typically lasts 2 to 4 months. Finally, the exogen (shedding) phase involves the release of old hairs. These durations can vary between individuals and hair location.

What can I do to support a healthy hair growth cycle?

To support a healthy hair growth cycle, focus on a balanced diet rich in essential nutrients, manage stress, get adequate sleep, and minimise harsh chemical or heat styling. Protecting your scalp health is also vital. Avoid aggressive brushing, which can lead to breakage. If you have specific concerns, consult a professional for personalised advice.

Is it possible to extend the anagen phase of hair growth?

While genetics primarily determine the length of the anagen phase, certain factors may help support its optimal duration. Maintaining good nutrition, managing stress, and addressing any underlying medical conditions can contribute to a healthy hair growth cycle. Some topical treatments and supplements are also designed to create an optimal environment for hair growth and potentially support a longer anagen phase, though results vary.

What's the difference between hair shedding and hair loss in relation to The Hair Growth Cycle?

Hair shedding is a normal part of The Hair Growth Cycle, specifically the exogen phase, where old hairs fall out to allow new ones to grow. Hair loss, however, implies that new hair isn't growing back as it should, or the new hair is weaker and finer. This could be due to a shortened anagen phase, follicular miniaturisation, or conditions preventing new growth.

Supporting The Hair Growth Cycle with Watermans

Watermans Haircare products are formulated with ingredients selected to create an optimal environment for healthy hair growth and to help reduce hair breakage, which can sometimes be confused with hair loss. Our products aim to support the hair's natural vitality and contribute to the appearance of fuller, stronger-feeling hair.

Key ingredients found in Watermans products, such as Biotin, Niacinamide, Caffeine, and Rosemary Extract, are known for their beneficial properties concerning scalp health and hair fibre strength. Biotin and Niacinamide, for instance, are B vitamins often associated with healthy hair. Caffeine and Rosemary Extract are frequently studied for their role in stimulating the scalp and promoting a healthy environment for hair follicles. These ingredients work together to help improve the appearance of hair density, condition, and overall strength.

For example, you will find Biotin, Niacinamide, and Rosemary Extract in our 'Grow Me' Shampoo and Conditioner. These are designed to nourish the scalp and hair from root to tip, helping to maintain healthy-looking hair and scalp, and making hair feel stronger. Zinc, another essential mineral for hair health, is available in our 'Grow More' Hair Vitamins, which are formulated to supplement your daily nutritional intake.

By incorporating Watermans products into your routine, you can provide your hair and scalp with beneficial ingredients that support their natural health and help reduce the appearance of shedding due to breakage, contributing to thicker, healthier-looking hair.

Sources and references

• American Academy of Dermatology Association, "Hair loss: Who gets and causes", aad.org
• National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institutes of Health, "Alopecia Areata: Questions and Answers", 2016, niams.nih.gov
• British Association of Dermatologists, "Hair loss (alopecia)", bad.org.uk
• Chew, E. G., & Maibach, H. I. (2018). Hair and scalp diseases: A medical and surgical approach. CRC Press. (Referenced for general hair physiology and cycle durations)
• Paus, R., & Cotsarelis, G. (2008). The biology of hair follicles. New England Journal of Medicine, 359(16), 1677-1686. (Referenced for detailed mechanisms of hair cycle phases)
• Murphrey, M. B., et al. (2023). Anatomy, Hair. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. (Referenced for hair anatomy and cycle overview)
• NHS, "Hair loss", nhs.uk
• Gavazzoni Dias, M. F. (2015). Hair cosmetics: An overview. International Journal of Trichology, 7(1), 2-15. (Referenced for general hair fibre health and cosmetic support claims)
• University of California San Francisco Health, "Hair Loss", ucsfhealth.org
• Mount Sinai Health System, "Telogen effluvium", mountsinai.org

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Find these ingredients in Watermans products

• Niacinamide: you will find this ingredient in our Hair Mask.