Hair Biology: The Hair Growth Cycle
The hair growth cycle is a continuous process of growth, regression, and rest that each hair follicle undergoes, crucial for understanding hair health and hair loss.
Understanding the Hair Growth Cycle
Each strand of hair on our head, and indeed across our entire body, undergoes a continuous process known as the hair growth cycle. This cycle is not synchronized across all hairs; at any given time, hairs are in different phases, which explains why we don't lose all our hair at once. Understanding this cycle is fundamental to comprehending hair health, hair loss, and the effectiveness of various treatments.
The hair follicle, a small organ in the skin, is responsible for producing hair. It operates autonomously, with each follicle having its own cycle. The length and characteristics of each phase vary depending on the type and location of the hair. For example, the hair on your scalp has a much longer growth phase than eyebrow or eyelash hair.
The Anagen Phase: Growing Hair
The anagen phase is the active growth phase of a hair follicle. During this period, the cells in the hair bulb, which is at the base of the follicle, divide rapidly, leading to the formation of new hair. The new hair pushes the old, club hair (a hair that has completed its growth phase) out of the follicle.
- Duration: This is the longest phase, typically lasting between two and seven years for scalp hair. Genetic factors, age, nutrition, and overall health significantly influence its duration.
- Characteristics: The hair is actively growing, gaining length, and is firmly anchored within the follicle.
- Importance: The longer a hair remains in the anagen phase, the longer it can grow. This is why people can achieve very long hair, while others, due to a shorter anagen phase, may struggle to grow their hair past a certain length.
At any given time, approximately 85-90% of the hairs on a healthy human scalp are in the anagen phase.
The Catagen Phase: Transitional Period
Following the anagen phase, the hair enters the catagen phase, a short transitional stage. This phase marks the end of active hair growth.
- Duration: This phase is relatively brief, lasting about two to three weeks.
- Characteristics: Hair growth stops, and the outer root sheath shrinks and detaches from the dermal papilla, which provides nutrients to the hair follicle. The hair bulb degenerates, and the follicle prepares for the resting phase. The hair strand is now known as a club hair.
- Physiology: The follicle begins to shrink, constricting the hair shaft and pushing it upwards. Only about 1% of scalp hairs are in the catagen phase at any given moment.
The Telogen Phase: Resting Hair
After the catagen phase, the hair follicle enters the telogen phase, its resting period. During this time, the hair is completely at rest, and no new hair growth occurs.
- Duration: This phase typically lasts for about two to four months.
- Characteristics: The club hair is fully formed and rests in the follicle. While it doesn't grow, it remains attached. Towards the end of this phase, the follicle becomes active again, and a new anagen hair begins to form beneath the club hair, eventually pushing it out.
- Hair Shedding: It is during the telogen phase that hair shedding occurs. On average, a person can shed 50-100 telogen hairs per day, which is a normal part of the hair renewal process.
Approximately 10-15% of scalp hairs are in the telogen phase.
The Exogen Phase: Continued Shedding (Sometimes Considered Part of Telogen)
Some trichologists recognize a distinct exogen phase, which is characterized by the active shedding of the club hair from the scalp. While often considered the latter part of the telogen phase, separating it emphasizes the mechanism of shedding.
- Mechanism: The new anagen hair grows in and pushes the old telogen hair out of the follicle. This is an active process rather than passive release.
Factors Affecting the Hair Growth Cycle
Numerous factors can influence the duration and health of each phase of the hair growth cycle. Any disruption can lead to issues such as hair thinning or hair loss.
| Factor | Impact on Hair Growth Cycle |
|---|---|
| Genetics | Predetermines growth cycle length and susceptibility to hair loss. |
| Age | Anagen phase shortens with age; follicles may miniaturize. |
| Nutrition | Deficiencies (e.g., iron, biotin, zinc) can disrupt growth and lead to shedding. |
| Stress | Can prematurely push hairs into catagen/telogen, leading to telogen effluvium. |
| Hormones | Androgens (testosterone, DHT) can miniaturize follicles in genetic hair loss. |
| Medications | Certain drugs (chemotherapy, blood thinners) can induce hair loss. |
| Scalp Health | Inflammation, infections, or poor circulation can impair follicle function. |
Watermans Hair products are formulated to support the hair growth cycle by providing essential nutrients and a healthy scalp environment, aiming to prolong the anagen phase and minimize premature shedding.
Disruptions to the Cycle
When the hair growth cycle is disrupted, it can manifest as various forms of hair loss. For example, in androgenetic alopecia (pattern baldness), the anagen phase progressively shortens, and the telogen phase lengthens, leading to increasingly shorter, finer, and miniaturized hairs.
Another common disruption is telogen effluvium, where a significant number of hairs prematurely enter the telogen phase due to a physiological stressor (e.g., severe illness, childbirth, extreme diet). This results in increased shedding several months after the triggering event.
Understanding the natural ebb and flow of the hair growth cycle provides a foundation for recognizing when hair loss is a normal physiological process versus when it may indicate an underlying issue that requires attention. Maintaining a healthy lifestyle, managing stress, and providing adequate nutrition are key components in supporting an optimal hair growth cycle.
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.