Monday, April 15, 2024
Hair lossHair Growth Phases

Hair Growth Phases

Keratinous fibers, which make up hair, are produced by follicles all over the body, except for the palms and soles, where there is no hair. When a person is born, they have a set number of follicles. The process of growing new hair is dynamic and can be broken down into four separate Hair Growth Phases. The length of these various stages and how they appear in different body regions are influenced by the duration of the multiple stages relative to one another.

Let’s take a more in-depth look at these four hair growth phases, the timeframes for each one, and why it’s vitally crucial for some of the hair to fall out while the process continues.

Even though hair falling out seems counterintuitive to healthy hair growth, it is actually a necessary part of the process. The cyclic shedding and regrowing of hair allow hair follicles to start fresh and produce new, healthy hair to replace old and damaged hair. If hair never fell out, damage would accumulate over time and hair quality would deteriorate.

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Hair Growth Phases

Anagen Phase

During this phase, the hair will grow at an average pace of approximately one-half inch per month. This growth is known as the active phase. The time spent in the anagen phase is directly proportional to the maximum hair length, and that measurement can range anywhere from 18 – 30 inches for most people. These  hair growth phases typically occur anywhere from two to six years apart.

The length of time hair spends in the anagen phase depends on genetics, health, age, and other factors. On average, scalp hair stays in this active growing phase for 2-6 years. Hair growth slows down with age, so the anagen phase shortens over time. This leads to thin, brittle hair in older adults.

Catagen Phase

After the growth phase of your hair is complete, it will enter a phase of transition called the catagen phase. To further clarify, what experts mean by “transition” is that this is the point in time when your hair will start the cycle of falling out.

While falling out sounds alarming, it is a normal part of the hair cycle. As hair reaches the end of its growing phase, it enters the catagen transition period before the old hair is shed and new hair starts growing. This lasts only about 10-15 days for scalp hair.

Although it can sound horrifying, the science around it is pretty fascinating. Your body sends a signal to the hair, telling it to stop developing, and in response, the hair follicles react by contracting slightly and separating from the blood flow. This process causes your hair to become thinner and less dense.

The catagen phase essentially

The catagen phase essentially cuts off nutrient supply to hair follicles to put them into a resting state. Detached from blood flow, the old hair starts thinning in preparation for shedding. However, new hair starts developing underneath to push the old hair up and eventually out, starting the cycle over again.

When you hear the word “detach,” you probably immediately think that this means your hair will start falling out in large amounts and that you will be bald for the rest of your life. The great news is that even while it separates from the scalp, the hair typically does not fall out till new hair starts to push it out and cause it to get dislodged.

Even in healthy people, hair loss is noticeable when combing or washing hair in the catagen/telogen phase when many hairs shed. But not to worry – new hair follicles are growing underneath to replace the lost hairs, keeping total numbers stable.

Telogen Phase

The telogen phase is a period of rest that the hair enters once it has finished detaching from the scalp. This is because your thinning hair will remain on the head for three to five months before new hair eventually pushes it out.

After detachment, scalp hair rests in the telogen phase for 3-4 months before shedding when the new anagen hair emerges underneath. Shedding 50-100 telogen hairs daily is normal. In some hair loss disorders, a high percentage of follicles prematurely enter telogen, causing excessive thinning of hair density.

This stage is, by no means, easy to complete. The term “telogen effluvium” was used by researchers at Harvard Medical School to characterize a particular ailment. This word is a fancy term describing the process in which a change in the body system or an unforeseen stressor causes the telogen phase to progress more quickly. In contrast to the average loss of 100 hairs per day, a person suffering from telogen effluvium may experience a loss of over 300 hairs daily.

In stressful events or after childbirth, as many as 70% of scalp hairs can rapidly enter telogen, shedding 300+ hairs daily. This excessive loss causes noticeable thinning. Though alarming, recovery normally occurs spontaneously within 6 months as hairs re-enter anagen growth.

Exogen Phase

When your hair finally reaches the exogen stage, it has already undergone many changes. The old hair separates from the scalp as the new hair comes in, and it then starts falling out in more significant numbers as the new hair takes its place. While you are most likely to notice this after you have combed your hair, you may also see clumps of hair in the shower drain or while you are styling your hair.

The exogen phase represents the final shedding stage when club hairs are ejected from the scalp after the new hair pushes upwards. These inactive hairs lacking color and elasticity are known as club hairs. Daily haircombing nicely coordinates exogenous shedding without excessive clumping.

How does hair loss affect the different hair growth phases?

Hair Growth Phases

The length of time a hair cycle takes might vary significantly from person to person. The reduction in the size of the hair follicles that occurs in bald men makes it more difficult for new hair to form.

Hair loss occurs when follicles shrink, shortening anagen growth below the 2 years needed to produce longer hair. This leaves follicles stuck perpetually in shortened cycles lacking anagen. Genetics regulates both follicle size and cycle duration, influencing male and female baldness.

According to recent research findings, an individual’s genetics are responsible for this stage reversal. Even if you have no control over whether or not you will be afflicted by it, you can prevent it from becoming worse by seeking treatment.

Androgens like testosterone and DHT activate genes, causing follicles in susceptible men to progressively miniaturize. Anti-androgens like finasteride help delay baldness. Though treatments exist, genetic regulation of hair cycling ultimately determines reversibility.

In what ways does treatment for hair loss influence these hair growth phases?

Finasteride and minoxidil are two medications approved by the FDA to prevent further hair loss.

Let’s briefly discuss DHT before moving on to the “how” part. DHT is a masculine sex hormone that usually assists in developing things like facial hair and muscle growth in the body. It starts by attaching itself to the hair follicles and gradually reducing their size until they cannot produce new hair follicles. DHT levels tend to be abnormal in males who have a condition known as male pattern baldness.

By blocking DHT, which shrinks hair follicles, finasteride promotes the maintenance of follicle size and cycling to sustain anagen growth. This helps stabilize hair loss in male pattern baldness. Without DHT signaling, follicles continue producing hair uninterrupted.

However, DHT is not the only factor in this process. It does this with the assistance of a companion enzyme known as 5′-reductase, just like every other villainous character does. Finasteride prevents 5′-reductase from ever developing in the body. Because of this, dihydrotestosterone (DHT) cannot receive the boost it requires to reduce the size of your hair follicles.

So finasteride works by inhibiting 5-alpha reductase to prevent the conversion of testosterone to DHT. With DHT levels lowered, hair follicles are rescued from shrinkage to maintain healthy anagen cycles.

Minoxidil, on the other hand, functions in a slightly different way. It helps increase the volume of anagen follicles (note that male pattern baldness occurs when the follicles get smaller) and reduces the time the telogen phase continues.

This indicates that your hair is becoming healthier and growing out at a faster rate. It also implies that you can experience something referred to as “minoxidil shedding” during the first few weeks after you begin utilizing it, but that is your older, thinner hair falling out to make room for new.

The Hormone That Leads to Hair Loss

An enzyme known as 5-alpha reductase converts testosterone into the hormone dihydrotestosterone, sometimes known as DHT. It is also possible to produce it from DHEA, a hormone more prevalent in females. The skin, as well as the hair follicles and the prostate, both contain DHT. Hair loss is brought on by both the acts that DHT performs and the susceptibility of follicles to DHT.

In addition, DHT affects the prostate. The prostate can’t develop normally in the absence of DHT. A man can get benign prostatic hypertrophy, often called an enlarged prostate, if he has excessive DHT in his body.


Although the rates at which people’s hair develops and falls out are unique, the stages that everyone passes through are the same. Because of this, awareness of each phase of hair development makes it much simpler to assess your personal hair loss and gives you a better understanding of how hair loss therapy could be of assistance.


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