Have you ever observed that body hair tends to stop growing after reaching a certain length? Similarly, have you noticed that the hair on your scalp exhibits a different growth pattern compared to body hair? Additionally, it’s interesting to recognize that not all hair strands regrow at the same pace after hair removal.
While it might seem surprising, the underlying reason for these variations in hair growth can be attributed to the hair growth cycle. This brings us to the essential questions: What exactly is the hair growth cycle, what phases does it encompass, and how does it function?
To provide a clearer understanding of the physiology, timeline, and mechanics involved in the hair growth cycle, we will delve deeper into the stages of hair growth.
Table of Contents:
Part 1: Understanding the Hair Growth Cycle
The hair growth cycle refers to the distinct phases that a hair strand undergoes, starting from its emergence until it eventually sheds. Typically, this cycle is divided into four key phases, which allow the hair on your scalp to grow for several years, while other hair may naturally shed.
Likewise, the various phases of the hair growth cycle on different parts of the body dictate not only the length and growth rate of hair but also how effective various hair removal techniques can be.
The four primary phases are: anagen, where hair actively grows; catagen, a transitional phase; telogen, a resting phase during which hair remains at its maximum length; and exogen, the phase when hair strands are shed.
Part 2: Detailed Stages of the Hair Growth Cycle
While you may be familiar with the terms describing the phases of the hair growth cycle, let’s examine each phase in more detail.
Anagen: The Active Growth Phase
The anagen phase is the first and most prolonged stage of the hair growth cycle. During this phase, hair can achieve its optimal length, provided it isn’t trimmed along the way.
At any given time, approximately 80 to 90% of hair is in the anagen phase.
Physiology of Anagen
Hair grows from follicles that receive a robust supply of blood from adjacent blood vessels. Additionally, hormones and hair growth factors play crucial roles in stimulating the follicles.
During the anagen phase, there is a rich influx of blood, growth factors, and essential nutrients toward the hair. Consequently, hair grows at its typical rate.
Timeline of Anagen
It’s vital to note that the duration of each phase in the hair growth cycle differs between the hair on the scalp and that on the body.
Catagen: The Transition Phase
While hair is firmly anchored to the follicle during anagen, it completely ceases growing in telogen. The catagen phase serves as a bridge between telogen and anagen.
Only about 3 to 5% of hair is in the catagen phase at any moment.
Physiology of Catagen
During the catagen phase, the blood supply to the hair follicles diminishes. Consequently, the hair follicle begins to shrink, leading to the detachment of the hair strand from the follicle. Hair may appear to be growing slightly during catagen, but it is simply surfacing after detachment.
Timeline of Catagen
The duration of the catagen phase is relatively consistent across different body areas, typically lasting between 1 to 2 weeks for both the body and scalp.
Telogen: The Resting Phase
Following the catagen phase is telogen, during which hair remains at the length acquired during anagen and catagen. Roughly 10 to 15% of hair on the body or scalp is in the telogen phase at any time.
Physiology of Telogen
In the telogen phase, hair growth completely halts. Hair strands do not receive any nutrients or growth factors, resulting in no further growth.
Timeline of Telogen
For hair on the scalp, the telogen phase can last approximately 100 days, or around 3 months. Conversely, hair on the body remains in telogen for only a few days.
Exogen: The Shedding Phase
Lastly, exogen marks the period when hair is shed from the follicles. Some experts consider this phase separate, while others view it as a continuation of the telogen phase.
Rather than focusing on a specific percentage, the number of hair strands in exogen is what matters, with typically only 40 to 120 strands shedding, constituting less than 1% of the total hair volume.
Physiology of Exogen
During exogen, two processes occur simultaneously: hair strands are falling from the follicles while the follicles prepare to produce new strands.
Timeline of Exogen
Similar to telogen, exogen lasts for a few months on the scalp, yet only a few days on the face and body.
Part 3: How Hair Growth Cycle Stages Influence Hair Removal Techniques
While we prefer hair to grow on our scalp for as long as possible, we generally want to eliminate unwanted hair from our face and body. Therefore, let’s explore how the different stages of the hair growth cycle can affect unwanted hair growth.
Effects of Hair Growth Cycle Phases on Shaving
Shavinghair removal
Anagen
In the anagen phase, hair is growing to its full extent. Although the visible part of the hair is on the surface, part of it remains beneath the skin. Thus, if you shave hair during the anagen phase, you may enjoy a smoother skin surface for a longer duration.
Furthermore, even when hair begins to regrow, its length will likely be shorter than usual, as part of the hair strand has already been trimmed.
Catagen
The effects of shaving in the catagen phase are similar to those experienced in anagen, but the duration is shorter compared to anagen.
For instance, if hair is shaved during catagen, it may take about a week to become visible again, while in telogen, it might take around two weeks.
Telogen
Should you shave unwanted hair during the telogen phase, it typically regrows within a few days, as the hair is already nearing its shedding period.
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