For many of us, our hair is inextricably linked to our identity and self-confidence. Whether you are actively trying to grow your hair longer or are concerned about increased shedding in the shower, understanding the biology behind your follicles is the first step toward effective management.
It is easy to assume that hair grows constantly until it is cut, but the reality is a complex, rhythmic biological process. Every single hair on your body operates independently according to a specific schedule known as the hair growth cycle.
At any given moment, your hair follicles are at different stages of this cycle. This asynchronous growth prevents us from shedding all our hair at once. However, disruptions to this cycle—caused by stress, nutrition, or genetics—can lead to noticeable hair thinning or loss.
In this article, we will explore the three primary phases of the hair growth cycle, the factors that influence them, and evidence-based strategies to maintain optimal hair health.
Overview of the Hair Growth Cycle
The average human scalp contains approximately 100,000 hair follicles. Beneath the skin, these follicles are surprisingly complex organs that regenerate themselves throughout your lifetime.
The life cycle of a hair strand consists of three distinct stages:
- Anagen: The active growth phase.
- Catagen: The transition phase.
- Telogen: The resting (and shedding) phase.
Understanding these mechanisms helps to demystify why hair falls out and how treatments typically work to prolong the growth period.
The Three Main Phases
1. Anagen (The Growth Phase)
The anagen phase is the period of active cell division and growth. This is the stage where the magic happens. The cells in the root of the hair divide rapidly, adding to the hair shaft and pushing it up through the skin.
During anagen, your hair grows around one centimetre every 28 days. This phase is the longest of the three, typically lasting anywhere from three to seven years for scalp hair. This duration largely determines the maximum length your hair can achieve.
Interestingly, the length of the anagen phase varies significantly across different body parts. Eyebrow and eyelash hairs have a much shorter anagen phase—lasting only a few months—which is why they never grow as long as the hair on your head.
According to the American Academy of Dermatology, at any specific time, about 90% of the hairs on your head are in this growth phase. The longer a hair stays in the anagen phase, the longer it will grow. As we age, the anagen phase often shortens, resulting in hair that becomes thinner and shorter with each cycle.
2. Catagen (The Transition Phase)
Following the active growth of anagen, the hair enters a short transitional stage called the catagen phase. This phase signals the end of active growth.
Lasting only two to three weeks, catagen is a period of rapid regression. During this time, the hair follicle shrinks significantly and detaches from the dermal papilla (the structure that supplies blood and nutrients). The hair becomes what is known as a ‘club hair’.
While the follicle cuts itself off from its blood supply, the hair shaft remains in place but stops growing. Approximately 1% to 3% of your hair is in the catagen phase at any given moment.
3. Telogen (The Resting Phase)
The final stage is the telogen phase, also known as the resting phase. This period usually lasts for around three months.
During telogen, the hair follicle is entirely at rest. The club hair is fully formed and remains in the follicle, but no active growth occurs. While the old hair rests, a new hair begins to form in the follicle beneath it, preparing to push the old one out.
It is estimated that 10% to 15% of scalp hair is in the telogen phase. If you notice hair in your brush or drain, it is likely these telogen hairs finally shedding. This specific shedding event is sometimes referred to by researchers as the exogen phase, though it is functionally part of the telogen termination.
It is perfectly normal to lose between 50 and 100 hairs per day during this phase. However, extreme stress or trauma can shock follicles into entering telogen prematurely, leading to a condition called telogen effluvium.
Summary of Phases
| Phase | Name | Duration | Status | Percentage of Hair |
|---|---|---|---|---|
| 1 | Anagen | 3–7 Years | Active Growth | ~90% |
| 2 | Catagen | 2–3 Weeks | Transition/Regression | ~1–3% |
| 3 | Telogen | 3 Months | Resting/Shedding | ~10–15% |
Factors Influencing the Cycle
While the hair growth cycle is a biological constant, various internal and external factors can alter the duration of each phase, often to the detriment of hair density.
Genetics and Ageing
Your genes play the most significant role in determining the length of your anagen phase. This is why some people can grow hair down to their waist, while others struggle to grow it past their shoulders.
As explained by the National Institutes of Health (NIH), ageing naturally causes the anagen phase to shorten and the follicles to miniaturise, leading to finer, shorter hair.
Hormonal Fluctuations
Hormones are powerful regulators of hair growth. Androgens (male sex hormones), particularly dihydrotestosterone (DHT), can shorten the anagen phase in genetically predisposed individuals. This process is the primary mechanism behind androgenetic alopecia, or pattern baldness.
Conversely, oestrogen tends to prolong the anagen phase. This is frequently observed during pregnancy, where high oestrogen levels keep hair in the growth phase, resulting in thicker locks. Postpartum, as hormone levels drop, many women experience significant shedding as those hairs enter telogen simultaneously.
Nutrition and Diet
The hair follicle is one of the most metabolically active sites in the body. Consequently, it requires a steady supply of energy, protein, vitamins, and minerals.
Deficiencies in iron, zinc, vitamin D, and protein can force hair out of the anagen phase and into the telogen phase. The Mayo Clinic highlights that poor nutrition is a reversible cause of hair shedding.
Stress and Illness
Physical trauma (such as surgery or high fever) and severe emotional stress raise cortisol levels. This stress response can signal hair follicles to prematurely stop growing and enter the resting phase. Shedding typically occurs three months after the stressful event.
Disorders Affecting the Cycle
When the cycle is disrupted, several clinical conditions may arise. Recognising these can help you seek appropriate treatment.
- Telogen Effluvium: A temporary condition where stress causes a large percentage of hairs to enter the resting phase. It results in diffuse thinning but rarely leads to total baldness.
- Anagen Effluvium: This involves the rapid shedding of hair during the growth phase, usually due to chemotherapy or radiation. Because the hair is lost during active growth, the shedding is often sudden and extensive.
- Alopecia Areata: An autoimmune disorder where the immune system attacks the anagen hair follicles, causing patchy hair loss. The British Association of Dermatologists provides extensive resources on managing this condition.
Treatment and Management
Supporting a healthy hair growth cycle involves a combination of lifestyle changes and, if necessary, medical intervention.
1. Topical Treatments
Minoxidil is one of the most common treatments for hair loss. It works by prolonging the anagen phase and increasing blood flow to the follicle, essentially ‘waking up’ dormant follicles. It is widely available and supported by substantial clinical data.
2. Nutritional Support
Ensuring you have adequate levels of ferritin (stored iron) is crucial. Iron is essential for the rapid cell division occurring in the hair bulb.
While biotin is a popular supplement, research suggests it is most effective only in those who have a true deficiency. For a balanced view, Healthline offers a comprehensive look at the efficacy of biotin for hair growth.
3. Scalp Care
A healthy scalp environment is vital for the hair growth cycle. Chronic inflammation, dandruff, or product buildup can clog follicles and impede growth. Regular cleansing and the use of anti-inflammatory ingredients like tea tree oil or ketoconazole can help.
Practical Tips for Healthy Hair
To keep your hair in the anagen phase for as long as possible and minimize damage during the delicate phases, consider the following habits:
- Gentle Handling: Wet hair is more elastic and prone to snapping. Avoid vigorous towel drying; instead, gently squeeze excess water out with a microfibre towel.
- Heat Management: Excessive heat can damage the hair shaft, leading to breakage that mimics hair loss. Always use a heat protectant spray.
- Massage: Some studies suggest that scalp massage can increase blood flow to the follicles, potentially stimulating the dermal papilla. The Cleveland Clinic notes that while not a cure-all, it promotes a healthy scalp environment.
- Stress Reduction: Practicing mindfulness, yoga, or regular exercise can lower cortisol levels, reducing the likelihood of stress-induced shedding.
The Bottom Line
The hair growth cycle is a fascinating, complex biological process that balances growth, regression, and rest. While genetics dictate the baseline duration of these phases, your lifestyle, diet, and overall health play pivotal roles in maintaining the cycle’s rhythm.
If you notice sudden, patchy, or excessive hair loss, it is vital to consult a healthcare professional or a dermatologist. They can help distinguish between a temporary disruption of the cycle (like telogen effluvium) and a condition requiring medical treatment.
Ultimately, patience is key. Because the hair cycle operates over months and years, any positive changes you make today may take three to six months to become visible. By treating your body with care and ensuring proper nutrition, you provide your follicles with the best possible foundation for long, healthy growth.
Additional Resources
- Structure of the Hair Follicle: Journal of Investigative Dermatology
- Understanding Hair Loss Types: Harvard Health Publishing
- Hair Loss Guide: NHS UK
- Anatomy of Hair: WebMD
