The Hair Growth Cycle: 4 Key Stages

Hair Structure

To understand human hair growth, let’s discuss its physiology. Your hair is made up of a complex protein called keratin. The keratinous part of your hair that you see, comb, and style every day is called the hair shaft, with hair follicles located just inside the scalp. 

Sebaceous glands (oil glands) open up into the follicle, helping to support the hair with moisture.

Hair growth occurs within the hair follicle, which lies deep below the epidermis, within the skin's dermis. Blood vessels richly nourish the base of each hair strand, providing the nutrients needed for growth. 

The hair shaft contains three layers:

• Cuticle: protects the hair.

• Cortex: contains the hair’s pigment and is the thickest part of the hair shaft.

• Medulla: determines the hair’s texture and thickness. Blonde and fine hair usually does not contain a medulla.

What Are the Stages of Hair Growth?

The phases of the hair growth cycle have been extensively studied, and each of the steps follows its own timeline. Every stage depends on the next to produce healthy hair growth and hair shedding cycles. When one phase in the process is disturbed, it may cause hair loss. 

Since each phase is active, your lifestyle choices can significantly affect the health of your hair. Androgens such as testosterone and other hormones also impact your hair growth. 

Below, we explore each of the hair growth phase and how your hair functions at each stage.

1: Anagen Phase (Hair Growth Phase)

Stage one of the hair growth cycle is the growth stage, called the anagen phase. Growth begins in the dermal papilla of the hair bulb, which provides blood supply and nourishment to each hair strand. 

During the anagen phase, the hair follicles continuously push outward, growing until each strand reaches the end of its lifespan or falls out. Ninety percent of the hairs on your head are in the active anagen phase at any given time.

Active growth lasts for two to seven years, depending on the individual. The time each strand spends in the anagen phase determines the hair strand’s length (aside from getting our hair cut or trimmed of course!).

The anagen phase for eyebrows, eyelashes, and other hair on your body is much shorter than the phase for the hair on your scalp. This is the reason for these shorter strands of hair. These hairs, also known as terminal hair, are usually more coarse than those on your head. 

2: Catagen Phase (Transition Phase)

Stage two of the hair growth cycle is known as the catagen phase. This is the transitional phase of the hair follicle, from growth to rest. The strands detach from the dermal papilla, decreasing the blood supply and the hair strand’s access to nourishment. 

This action signals the hair strands to stop growing, which transitions the hair to what is called  “club hair.” Club hairs contain a bulb of keratin at the tip of the hair strand’s root. This bulb helps keep the hair shaft inside the follicle until it eventually sheds in the next phase. The catagen phase lasts about two weeks.

3: Telogen (Resting Phase)

The telogen phase is the dormant phase for the hair strand. During the telogen resting phase, the hair undergoes a period of inactivity which lasts up to four months. Some hair may fall, but new hairs are preparing for growth.

4: Exogen Phase (Release Phase)

The exogen phase occurs within the telogen phase, which causes scalp hair shedding. After the exogen hair detaches from the scalp, the hair follicle re-enters the anagen phase, and the regrowth cycle begins again. 

What Is Hair Fall?

Hair fall, also known as hair shedding, refers to the average amount of hair you lose daily. You lose roughly 50 to 100 hairs per day. 

This hair fall is a normal part of the hair growth cycle. It occurs during exogen and immediately transitions to hair regrowth or the anagen phase. 

Common Types of Hair Loss

Different from hair fall, hair loss is a widespread condition that dermatologists frequently diagnose and treat. It is not contagious, although some health conditions may lead to hair loss. Various hair care products can help support hair strength, but some conditions cannot be treated. 

More severe cases may require help from a hair restoration physician or dermatology office. These facilities provide stem cell hair therapy and transplantation treatments. The more costly treatments work to relocate hair follicles and restore hair growth for long-lasting results. 

A few common types of hair loss include:

1. Telogen Effluvium

Excessive hair loss is known as hair shedding or telogen effluvium. This nonscarring medical condition often ceases on its own and results from stressors such as:

• Weight loss of more than 20 pounds

• Childbirth

• Severe or chronic illness and high fever

• Cessation of birth control pills

• Medications

• Chemotherapy

• Surgery

• Iron Deficiency

Telogen effluvium occurs several months after a stressful event. It often ceases within six to nine months after the stressful event has ended. This condition occurs when the hairs enter the telogen phase prematurely. Telogen effluvium is temporary and may be acute or chronic.

2. Central centrifugal cicatricial alopecia (CCCA)

This type of hair loss affects the scalp with scarring. It involves inflammation and noticeable hair loss at the crown’s center. CCCA destroys the hair follicles, leaving behind irreversible scarring. 

This follicle scarring produces a smooth-feeling area on the skin. Early treatments can prevent CCCA from spreading and causing a broader scope of hair loss by encouraging hair regrowth before the follicle is destroyed. 

3. Involution Alopecia

Involution alopecia is one of the most common types of hair loss for both men and women. It involves the gradual thinning of hair due to genetics and age. Hair strands remain in the anagen phase for a reduced amount of time, thus causing shorter hair strands. 

Over time, the hair follicles begin to thin and prematurely transition to the telogen phase. They remain in that state until the hair falls out. This type of hair loss is not preventable.

4. Alopecia Areata

Alopecia areata is a type of hair loss that results in clumps of hair falling out. This autoimmune disease appears in men and women of all ages and races, affecting roughly 6.8 million people in the U.S. and 147 million worldwide. You may remember Jada Pinkett Smith, who publicly announced her diagnosis of alopecia areata in 2018.

This type of follicular hair loss results from an autoimmune disease that attacks the hair follicles, causing circular bald patches. Fortunately, alopecia areata can be treated, and hair regrowth is possible. When the hair regrows, it may be permanent or fall out again. 

There are three main types of alopecia:

• Alopecia areata: Patchy baldness occurring anywhere on the body, including the scalp, armpits, beard, eyelashes, and eyebrows 

• Alopecia totalis: Complete baldness on the scalp

• Alopecia universalis: Rare condition of complete baldness on the entire body and scalp

5. Traction Alopecia

Traction alopecia is caused by the continuous pulling of the hair root, resulting in cuticle breakage. It is also caused by over-styling your hair, wearing tight braids, buns, or ponytails, using harsh hair coloring dyes, or overuse of heated styling tools. 

This over-styling causes damage to the hair follicles, resulting in irregular breakage, epidermal friction, and hair loss. Traction alopecia may cause permanent hair loss over time, but with proper precaution, it is a preventable condition. 

6. Androgenetic Alopecia 

Androgenetic alopecia is the most common type of alopecia, affecting both men and women. This condition is often called male pattern baldness, and for women, female pattern baldness. 

Androgenetic alopecia is permanent hair loss caused by genetics. It is characterized by a receding hairline at the crown or over the entire scalp. 

Men may experience this genetic hair loss as early as their 20s. In comparison, women don’t experience it until their 40s or later. 

How To Regrow Hair 

• Specially formulated shampoo and conditioner to promote scalp health

• Minoxidil treatments

• Hair bond treatments 

• Certain supplements made with ingredients known to support healthy hair growth

• Scalp massage

• Avoiding hair chemical treatments

• Eating a balanced diet 

• Increasing vitamin intake

• Reducing heated styling

What to Do Next?