Hair Growth Cycle

The hair growth cycle is key to understanding the purpose and efficacy of hair loss treatments whether it be medicinal or surgical. Hair typically grows half an inch per month, or about 6 inches per year. The hair cycle occurs in three distinct phases: anagen, catagen, and telogen.

The Anagen Phase

The anagen phase is the active growth phase of the hair growth cycle. During this phase, the cells in the hair bulb at the base of the hair follicle are rapidly dividing and producing new hair. This new hair pushes the older hair out of the follicle, which is then shed. The anagen phase can last for several years and the length of this phase can vary depending on genetics, age and other factors. Different hair on different parts of the body have different lengths of the anagen phase, which is why eyebrow and beard hair do not grow as long as head hair.

During the anagen phase, the hair follicles are supplied with a rich blood supply, which provides the necessary nutrients for hair growth. The cells in the hair bulb also contain the pigmentation that gives the hair its color. The length of the anagen phase determines the potential length of the hair, and the sooner it finishes the shorter the hair will be.

The Catagen Phase

The catagen phase is a transition phase in which hair growth ultimately stops. The base of the hair shaft will shrink and eventually separate from the hair follicle, yet will remain in place for one to two weeks. The catagen phase is the shortest phase of the hair cycle.

The Telogen Phase

The telogen phase is the final phase of the hair growth cycle, also known as the resting phase. In this phase, the hair strand that was formed during the anagen phase is shed, and hair bulb gathers nutrients until it is ready to begin the cycle anew. During the telogen phase, the hair follicle is not actively producing new hair, and the hair strand attached to the follicle is in a dormant state. The length of the telogen phase can vary, but it typically lasts for several weeks to a few months.

Normally, about 10-15% of the hair on a person's scalp is in the telogen phase at any given time. However, certain factors can cause an increase in the number of hair strands entering the telogen phase, resulting in hair loss. These factors can include stress, hormonal changes, certain medications, and certain medical conditions. It is important to note that hair loss during the telogen phase is a normal process, and it's not always a sign of a health issue. However, excessive hair loss or hair thinning may indicate prolonged activity in this phase and may ultimately point to hair miniaturization.

The Causes of Hair Loss

Many factors such as stress, hormonal changes, and family history may contribute to male pattern hair loss. No two cases of hair loss are identical, and it is important to be aware of the factors that may be affecting you.


Hormones play a significant role in hair loss, specifically the hormone dihydrotestosterone (DHT). DHT is a metabolite of testosterone, and it is produced by the action of an enzyme called 5-alpha reductase on testosterone. DHT attaches to receptors on the hair follicles, causing them to shrink and eventually become unable to produce new hair. The severity of hair loss and whether miniaturizaiton will result in general thinning, receding, or baldness is dependent on a person’s genetic makeup. However, the mechanism of hair loss in androgenic alopecia is dictated by the prevalence of DHT.


Hair loss, also known as androgenetic alopecia, is a primarily a genetic condition that enables hormonal interactions that result in hair loss. The genetic component of hair loss is inherited from one's parents, and it is determined by the presence of certain genes that make a person more susceptible to hair loss.

The main gene associated with hair loss is the androgen receptor gene, which is located on the X chromosome. If a person inherits one or two copies of this gene from their parents, they are more likely to experience hair loss. The presence of this gene makes the hair follicles more sensitive to the effects of the hormone dihydrotestosterone (DHT) It is important to note that the presence of these genes does not guarantee hair loss. Other factors, such as hormonal changes and age, also play a role in the development of hair loss.

Symptoms of Hair Loss

The symptoms of hair loss can vary depending on the type and cause of the hair loss. Some men might notice hair thinning starting at the hairline and temples, while others may have their hair loss start in the center or crown. Abnormally excessive shedding may be a sign of hair loss, and is most commonly noticed on pillows or in the shower. This indicates hairs are not remaining in their growth phase and instead are shedding, most likely due to nutrient deficiencies within the hair follicles. Hairs may eventually move beyond thinning and result in empty spots, which indicates telogen hairs have not replaced the lost hair. Over enough successive cycles, the affected hairs will atrophy the point of complete loss.

The Norwood Scale

The Norwood scale is a classification system used to describe the different stages of male pattern baldness. The scale was developed by Dr. James Hamilton in the 1950s and later modified by Dr. O'Tar Norwood in the 1970s.

The Norwood scale consists of seven stages, with stage 1 being the least severe and stage 7 being the most severe. Each stage is characterized by a specific pattern of hair loss, and the scale is used to help determine the appropriate treatment for hair loss. There are also subcategories that distinguish the type of stage into A and B categories.

It is important to note that no hair loss scale is perfect, and the Norwood scale is merely a tool that can help determine the extent of hair loss and how aggressive the pattern is relative to the age of the patient. As health care professionals, we do not dictate medical interventions by way of a hair loss scale. Every patient is different and their condition unique, and this necessitates customization every step of the way.

Excellence in the Art of Hair Transplantation

Hair transplantation is a hair restoration surgery that works by moving hair from the back and sides of your head to the thinning or balding areas on the top of your scalp.
Dr. Koher and the surgeons of Koher Medical are particularly experienced with this procedure, having over 35 years of experience and having performed over 15,000 hair transplants nationally and internationally.

If you’re looking for a solution to your hair loss, you can trust the surgeons and staff of Koher Medical to deliver a world class experience and state of the art cosmetic results. No matter what your hair loss situation, Koher Medical is ready and willing to offer our expertise and years of experience.