Hair Loss Causes – Understanding Hair Growth

The Four Stages of Hair Growth – How Hair Works

The Four Stages of Hair Growth Explained

To understand why balding and hair loss happens in men and women, it is first helpful to understand how hair grows and what happens during each phase of the hair growth cycle. The hair growth cycle is comprised of four distinct stages: the Anagen phase, the Catagen phase, the Telogen phase, and the Exogen phase. The process of hair growth, shedding, and renewal occurs by means of these four phases in the hair development and growth cycle. There are also multiple factors which can interrupt the hair growth cycle and cause thinning hair and hair loss, the most common of which is androgenetic alopecia, or hereditary pattern baldness.

stages cycles of hair growth

Anagen: The Growth Phase

The Anagen stage of hair growth occurs in approximately 90 percent of a person’s hair follicles at any one point in time. The Anagen phase of hair growth is the development period in the hair growth cycle and can last for approximately two to six years. In this stage of hair growth, the hair follicles most commonly grow at a rate of about one centimeter per month.

Catagen: The Regression Stage

The second stage of hair growth is known as the Catagen phase of the cycle. In the Catagen phase, hair follicles recede and diminish into a smaller version of themselves. The Catagen phase is quite short, lasting generally from two to four weeks. The blood supply to the hair follicles is reduced, creating what is known as “club hair,” after which the normal cycle is for this hair to be shed.

Telogen: The Resting Phase

The last phase in the hair growth cycle is the Telogen phase, or the resting stage. Roughly 5% to 15% of your scalp’s follicles are in the Telogen phase at any given time. Up to 200 “club” hairs can be shed in a day. The Telogen phase of the hair growth cycle is where you may see more hairs than expected on your pillowcase when you get up in the morning.

Exogen: The Hair Shedding Phase

The exogen phase of the hair growth cycle is really just an extension of the telogen phase. During this phase, hairs are actually shed from the scalp. This often occurs when you are brushing, styling, or washing your hair.  It is normal for men and women to lose 50-100 hairs per day during this phase. The exogen phase can last from two to five months during which time new hairs are beginning to grow in the follicles as old hairs are shed.

What Happens During Hair Loss?

For the vast majority of men and women, hair loss and thinning hair is caused by androgenetic alopecia or pattern baldness. Androgenetic alopecia can affect up to 95% of men and over 50% of women. As its name implies, androgenetic alopecia is genetic or hereditary in origin and cause. In the case of androgenetic alopecia, the new hair growth becomes finer and weaker until new hair growth ceases in the affected area.

A second and increasingly more common form of hair loss in men and women is telogen effluvium or stresss-related hair loss.  This can occur when there is an abnormal amount of stress placed on the body’s central nervous system, such as during childbirth or as a result of the body’s exposure to and recovery from Covid-19. Telogen effluvium has been noted in a number of cases of prolonged symptoms of Covid 19 or long Covid.

Is Hair Loss Permanent?

Depending upon its cause and nature, hair loss (alopecia) can be permanent or temporary. It can affect just a person’s scalp area, or it can affect the individual’s entire body. There are FDA approved treatments to help restore normal new hair growth which may be helpful to individuals experiencing androgenetic alopecia. These may include topical hair loss treatments, as well as therapies such as low-level laser hair therapy, PRP hair therapy, A-Cell therapy, and others.

It is important to realize, however, that these treatments only work where new hair growth is possible. Once new hair growth ceases to occur and the hair follicle dies, hair loss treatments no longer work, since there is no hair left to treat.

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