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Stages of Hair Growth and Loss

Stages of Hair Growth and Loss

It should come as no surprise that the hair on your scalp grows at a rate of approximately six inches per year. What you may not have known is that hair growth occurs in three distinct phases and that not all of the hair on your head is in the same phase at the same time.

Three Phases of Hair Growth 

• Anagen - This is the active growth phase, when the cells at the root of the hair divide rapidly. Approximately 80% to 85% of the hair is in the anagen phase at any one time. Scalp hair remains in this phase for anywhere from 2 to 6 years, growing at a rate of roughly 1 centimeter every 8 days. The duration of the anagen phase of hair growth is genetically determined and tends to last longer in people of Asian origin.
• Catagen - At the end of the anagen phase, the catagen phase begins. This is a brief transitional period lasting for about 10 days. During this period, the follicles get a chance to chill out and replenish themselves. Follicles recede to around 1/6 their original length, causing the shaft of the hair to be pushed upward. Around 3% of all hairs are in the catagen phase at any one time.
• Telogen - This is a resting phase and lasts for around 100 days, or a little longer than 3 months. Between 10 and 25 hairs in the telogen phase are lost each day.

Why Chemotherapy Causes Hair Loss

During the growth phase of hair, anagen, the cells in the hair root are growing and dividing very rapidly. Chemotherapy drugs are designed to target rapidly-dividing cancer cells. This brings the hair cells out of the anagen phase and into the catagen phase, followed by the resting phase. Hair can enter back into the anagen phase within a few weeks after completing treatment, although the density of the new hair may not be the same as before.

At the moment, there are no guaranteed ways of preventing hair loss following chemotherapy, although several methods are being developed. These are:

• Scalp hypothermia (cryotherapy) - While a patient is undergoing chemotherapy, the scalp is chilled using ice packs or other paraphernalia. This reduces blood flow and hence the delivery of chemotherapeutic drugs to the area. The downside of this treatment is that the scalp receives a lower amount of drug, making it potentially vulnerable to developing cancer in the scalp. Patients also report that it is cold and uncomfortable.
• Minoxidil – Available over the counter in a 2% or 5% solution, Minoxidil is a drug developed to prevent hair loss that comes in a spray or a lotion.  Originally developed to treat high blood pressure, this popular hair loss treatment is now used to combat the most common form of hair loss, genetic hair loss.  While it is unclear exactly how Minoxidil affects hair growth it does appear that the medicine increases hair follicles and can also make existing hair thicker.  Please consult your doctor before beginning to use Minoxidil as it does have reported side effects.

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