Hair Loss Cycle
The Stages of the Hair Growth and Hair Loss cycle
Hair growth and hair loss are part of a natural cycle that everyone experiences. Disruptions to this cycle can lead to noticeable thinning and shedding.
Hair growth can be broken into 4 key phases:
Anagen – Growth Phase
Catagen – Transition Phase
Telogen – Resting Phase
Exogen – Shedding Phase
Proper understanding of the growth and hair loss cycle offers a foundation for identifying issues and supporting healthy regrowth.
Growth Phase
The active phase where new hair is produced, lasting 2-7 years
Transition Phase
A brief phase lasting 2-3 weeks when hair growth stops, and the follicle begins to shrink
Resting Phase
A dormant period of about 3 months when the follicle rests, and the hair remains in place before shedding
Shedding Phase
The final stage where old hairs are shed, making way for new hairs to grow in the next cycle
Hair grows and sheds according to a natural cycle that plays a vital role in overall hair health. This cycle includes four distinct phases: growth (anagen), transition (catagen), rest (telogen), and shedding (exogen). Each phase has its own function and timing. Under normal conditions, this process keeps hair renewal balanced. Factors like stress, hormones, ageing, or illness can disrupt this cycle, leading to increased shedding or thinning. Understanding how the hair growth and loss cycle works is key to recognizing what’s normal, identifying potential problems, and taking the right steps to support healthy regrowth.
Genetic Predisposition
Genetic predisposition is one of the most common causes of hair loss, which impacts both men and women. Androgenetic alopecia, or male pattern baldness, is caused by inherited traits passed down through family genes. These traits lead to sensitivity to hormones like dihydrotestosterone (DHT), which causes hair follicles to shrink over time. This is visible as gradually thinning hair, followed by hair loss and balding. Understanding the genetic risk to hair loss can help with proactive steps to manage and slow down the progression.
Hormonal Influence
Numerous studies have identified specific genetic markers associated with androgenetic alopecia. A study published in the journal Nature Communications in 2017 identified over 200 genetic loci linked to male pattern baldness. These findings highlight the hereditary nature of AGA.
Role of Androgen Receptor Gene
The androgen receptor gene is located on the X chromosome and plays a crucial role in AGA. A study published in the journal JAMA Dermatology in 2013 showed that variations in this gene can influence susceptibility to AGA, which impacts the hair growth cycle.
Hormonal Influence
Hormones play an important role in hair loss. Hormones like dihydrotestosterone (DHT), a byproduct of testosterone, can bind to hair follicles causing them to shrink. Other hormonal shifts, such as thyroid disorders, can disrupt the hair growth cycle and result in excessive shedding or thinning. Recognizing the hormonal influence is key to identifying effective treatment options.
The Role of Dihydrotestosterone (DHT)
Dihydrotestosterone (DHT) is a potent androgen derived from testosterone. DHT leads to a process known as miniaturization within the hair growth cycle. A study published in the journal Dermatology in 2020 investigated the correlation between DHT levels and AGA severity, providing insights into the hormonal aspects of the condition.
Sensitivity of Hair Follicles
Hair follicles are not all equally as sensitive to DHT. Some follicles are genetically predisposed to be more sensitive, leading to miniaturizing during the growth cycle. Research published in the Journal of Clinical Investigation in 2019 identified specific androgen receptor genes responsible for regulating hair growth.
Follicular Miniaturization
The primary process behind hair thinning and hair loss is follicular miniaturization. This occurs when hair follicles gradually shrink in size, producing thinner, shorter, and less pigmented hair over time. Eventually the follicles can stop producing hair completely, leading to balding. Understanding the miniaturization process is important to assist with treatments to maintain and restore the hair follicle health.
Progressive Hair Thinning
The biggest sign of hair loss is the gradual thinning of hair shafts within the hair growth cycle. Over time, the affected hair follicles produce thinner, shorter hair. This is done through the miniaturization process, which disrupts the hair growth cycle.
Shrinking of Hair Follicles
The miniaturization within the hair growth cycle is accompanied by the shrinking of hair follicles. As the hair follicles become smaller, they produce increasingly fine and weak hairs. This process will eventually lead to the cessation of hair growth altogether.
Impact on Hair Growth Cycle
The miniaturized hair follicles will have a shortened anagen (growth) phase and an extended telogen (resting) phase within the cycle. This disruption in the hair growth cycle results in a progressive reduction in hair density and overall coverage.
Hair Growth and hair loss Cycle
The natural hair growth cycle consists of 4 phases, anagen, catagen, telogen, and exogen. Understanding these phases, and what takes place in each, is helpful to understand how disruptions in the cycle impact hair loss.
Anagen Phase (Growth Phase)
The anagen phase is the active growth period of the hair cycle and can last from 2 to 7 years. During this phase, hair follicles are fully functional and produce hair at an average rate of half an inch per month. The maximum length of hair for someone is dependent on the length of the anagen phase. In conditions like androgenetic alopecia, the anagen phase becomes progressively shorter. This leads to thinner, weaker hair, and eventually hair loss.
Catagen Phase (Transition Phase)
This phase marks the end of the active growth period and lasts for 2 to 3 weeks. During this phase, hair follicles shrink, and the hair detaches from the blood supply, transitioning to a resting phase. The catagen phase is a normal part of the hair growth cycle, but disruptions, such as stress or illness, can prematurely push hairs into this phase. This interruption in the cycle can lead to increased shedding and thinning.
Telogen Phase (Resting Phase)
The telogen phase is a resting period that lasts for approximately 3 months. During this phase, the hair remains in the follicle but is no longer actively growing. At the end of this phase, new hair will begin to grow and push out the old hair, leading to natural shedding. If excessive shedding occurs, it may indicate conditions like telogen effluvium. This is where a higher percentage of hairs enter this phase simultaneously due to stress or illness.
Exogen Phase (Shedding Phase)
The final phase in the hair loss cycle is the exogen phase, a sub-phase of telogen, where old hair is shed from the scalp to make room for new growth. It’s normal to lose 50-100 hairs daily during the exogen phase. Factors like genetics, hormonal imbalances, or scalp conditions can increase shedding beyond the expected levels, contributing to visible hair loss.
Normal Shedding vs Excessive Shedding
It’s normal, and expected, to lose hair every day. Most people will experience a shed of 50-100 hairs daily as part of the natural hair growth cycle. This shedding occurs during the exogen phase, when old hairs are pushed out to make room for new hair growth. Under normal conditions, the shedding is visibly unnoticeable because the new regrowth balances the shed hairs. Hair naturally cycles through the growth, transition, rest, and shedding phases, so minor shedding is part of the process.
Excessive hair shedding, outside of normal levels, can be a sign of androgenetic alopecia, also known as male pattern baldness. This condition is caused by a gradual shortening of the anagen (growth) phase, and prolonged telogen (resting) phase. Over time, the affected hair follicles will shrink, producing thinner and shorter hair, until they eventually stop producing hair altogether. Unlike normal shedding, excessive shedding may be noticeable as clumps of hair in the shower or on the pillow. If there is excessive shedding, this will lead to visible changes in your appearance, with the hairline thinning or receding.
FAQ
What are the main causes of hair loss?
Hair loss can result from various factors, including genetics (androgenetic alopecia), hormonal imbalances, stress, nutritional deficiencies, medical conditions (e.g., thyroid disorders), and certain medications. Identifying the cause is crucial for determining the right treatment.
What are the stages of the hair growth cycle?
The hair growth cycle consists of four main stages:
- Anagen (Growth Phase): This is the active phase where hair grows from the follicle. It lasts 2–7 years, depending on genetics.
- Catagen (Transition Phase): The follicle shrinks, and hair growth slows. This phase lasts 2–3 weeks.
- Telogen (Resting Phase): The hair follicle remains dormant, and no new growth occurs. It lasts about 3 months.
- Exogen (Shedding Phase): Old hair sheds to make way for new growth.
How can I tell if my hair loss is temporary or permanent?
Temporary hair loss, such as telogen effluvium, often results from stress, illness, or hormonal shifts and can resolve once the underlying cause is addressed. Permanent hair loss, like androgenetic alopecia, progresses over time without treatment. Consulting a dermatologist can help determine the cause.
What is the relationship between hair loss and the hair growth cycle?
Hair loss occurs when the balance of the growth cycle is disrupted. For example, in conditions like telogen effluvium, more hairs enter the telogen phase prematurely, leading to increased shedding. In androgenetic alopecia, the anagen phase shortens, and hair follicles produce thinner, weaker hairs.
Can I promote the anagen (growth) phase of the hair cycle?
Yes, maintaining a healthy lifestyle with proper nutrition, reducing stress, and using hair growth treatments like minoxidil can help support the anagen phase. These strategies encourage stronger, more prolonged hair growth.
Conclusion
Hair loss can have different underlying causes, including genetics and hormones, that will cause disruption to the normal hair growth cycle. These disruptions will shorten the anagen phase and extend the telogen phase, leading to visible hair loss. To reduce or stop hair loss, treatments need to be able stop the interruption of the growth cycle allowing it to return to normal. Treatment options can vary depending on the cause of the hair cycle disruption.
Want to Learn More?
Click to view the latest scientific paper on Male Androgenetic Alopecia from the National Library of Medicine.
