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Understanding Hair Loss Through the Hair Cycle

 Hair loss is best understood if you know all about the hair cycle. Contrary to popular belief, hair doesn’t grow continuously all in one go. Hair undergoes changes as it enters a new phase in the hair growth cycle.

This post will introduce you to the important hair parts and the hair cycle. We’ll also explain where hair loss typically fits in these stages.

The Hair Structure

Hair is typically made of two parts, namely:

1. Hair Follicle

The hair follicle lies on the scalp with the primary function of anchoring the hair through the scalp. Hair follicles are comprised of two parts, the bulb and the papilla.

The bulb houses the hair cells that allow a hair strand to grow. It is located at the bottom part of the hair follicle. It is also in the bulb where we can find:

  • Sebaceous glands – Tiny structures that secrete oil
  • Arrector pili muscle – Leaf-like muscles that cause hair to go up when they contract

The papilla lies beneath the bulb and contains tiny capillaries that provide blood supply to the entire hair follicle. Good blood supply coming from the papilla encourages healthier hair growth at the follicular level.

Fact: The average number of active hair follicles on the scalp is around 100,000. That’s a lot of hair strands to start with! And we don’t generate new hair follicles – all of these follicles are present in a developing fetus’s 22nd week of life.

2. Hair Shaft

This is the visible hair we see growing out of our scalp. The hair shaft is deeply rooted in the follicle and grows out of it until it reaches outside the scalp.

Hair shafts are made of a protein called keratin. This is a tough protein that serves as your hair’s structural building block.

The shaft is also protected by another layer of the hair called cuticle. It is the outermost layer made up of overlapping dead cells, forming scales to protect and strengthen the hair shaft. It is a usually colorless and thin yet tough layer.

Fact: The actual hair that we all sport on our head is actually the cuticle’s dead cells!

Now that we know the two main parts of hair, let’s move on to the stages of hair growth.

The Three Stages of the Hair Cycle

Hair grows at a rate of ½ inch per month. That’s almost 6 inches of hair growth in a year. Also, hair appears to grow faster during the summer months and goes slower during winter.

All these things happen due to the influence of the hair growth cycle.

Here’s a look at the three stages that comprise it:

  • Stage One: The Anagen Phase

This stage is dubbed the active period of hair growth. Cells on the bulb of the hair are actively dividing at a fast rate, leading to new hair production. This new hair then pushes existing hairs up and outside the hair follicles. Old hairs that are not in the anagen phase are also known as club hairs.

The anagen phase can cause hair growth for around 2-6 years, and cause hair to grow to lengths of 18-30 inches. Every 28 days, hair can possibly grow up to 1 cm in length.

The length of the anagen phase widely varies among different people. Some people have naturally longer anagen phases, causing them to grow very long head hair. Others may see only a small amount of growth due to their naturally short anagen phases.

  • Stage Two: The Catagen Phase 

The catagen phase is a short period that lasts only 2-3 weeks. This period is characterized by the rapidly-dividing cells slowly come to a halt. The hair then detaches itself from the capillaries in the hair papilla, forming what is known as club hair.

The onset of catagen is triggered by a protein called Fibroblast Growth Factor 5. It is mostly produced in the hair follicle’s outer sheath and increases during the later part of the anagen phase. Its presence in the hair follicles signals the transition from anagen to catagen.

  • Stage Three: The Telogen Phase

The telogen phase is the final stage characterized by the complete resting period of the hair follicle. Club hair formation is completed at this time.

Shedding is typical in the telogen phase as the resting club hair is being released from the hair follicles. You would notice that a fallen or pulled-out hair in the telogen phase has a white, dry, and solid material attached to the root.

The empty hair follicles will then get ready for the new growth of hair come anagen phase again.

Your entire scalp doesn’t go into the telogen phase all at once. Around 6-8% of the hairs on your head are in the telogen phase at any point in time. This is why you normally shed 25-100 hairs daily.

The telogen phase lasts for three months. After this, the hair goes back to the active growth period of the anagen phase.

Where Does Hair Loss Fit In?

Hair loss can typically come anywhere inside the hair growth cycle. A variety of factors can influence your susceptibility to hair loss, especially in the telogen phase of the hair cycle. Such factors include the following:

  • Poor nutritional status
  • Mental disposition
  • Long-term exposure to stress
  • Stress coping mechanisms
  • Hormonal imbalances
  • Medication use
  • Overuse of chemical hair treatments and coloring
  • Chemotherapy
  • Chemical exposure
  • Thyroid illnesses
  • Other medical illnesses
  • Generalized and localized skin conditions
  • Bacterial or fungal infections
This lengthy list of factors influencing hair loss can happen anytime during the hair cycle. They are often responsible for conditions such as female/male pattern baldness, postpartum hair loss, alopecia areata, androgenetic alopecia, and others.

However, there are hair loss conditions that affect certain phases of the hair growth cycle. These are the following:

  • Anagen effluvium

 This is hair loss caused by exposure to strong medical treatments, such as in chemotherapy. It often coincides during the anagen phase of the hair cycle as the strong medications may also shut down hair production at the follicles.

  • Loose Anagen Syndrome

A hair loss condition affecting children, wherein hair can be easily pulled out due to it not being rooted firmly at the follicles. Hair can easily fall out even when it is actively growing.

  • Telogen Effluvium

A large number of hair follicles enter the telogen phase, but the next growth phase of the anagen period fails to start. 300-500 hairs are expected to fall daily with this condition. Telogen effluvium is often the result of a medical event such as surgeries and thyroid imbalances. However, it is closely associated with postpartum hair loss.

Most of the treatments addressing these hair loss problems now focus on lengthening the anagen phase to boost hair growth.

The Wrap Up

Hair goes through three cycles in order for it to grow normally. These are:

  • Anagen phase – Growth phase
  • Catagen phase – Transitional phase
  • Telogen phase – Resting phase

Various changes in the hair follicles, blood supply, and hair shaft happen during each phase. All of these changes lead to the normal shedding and hair growth processes of the scalp.

Hair loss conditions may occur at any phase of the hair cycle. But there are certain conditions that mostly affect hair in the anagen and telogen phases. As such, you and your doctor can tailor your treatment course and hair care routines keeping in mind the phases where your hair currently is.

Any questions on the hair growth cycle? Or have you experienced a hair loss condition associated with the hair cycle? Tell us in the comments section below!


  1. Interesting info about hair science. Thanks for this �� Your blog is informational as always :D


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