The hair on the human scalp grows in a specific pattern and has an established growth cycle. This cycle results in periods of hair growth and shedding. The structure of the hair prevents damage to each hair region and contributes to normal growth. Understanding the structure and growth cycle of hair helps you take better care of your hair and gives you the knowledge you need to identify hair problems.
Features
Hair consists of keratin and has cuticle, medulla and cortex regions. The cuticle consists of scales that cover the hair shaft. These scales include spinous scales, coronal scales and imbricate scales. Coronal scales usually appear in rodent and bat hair, but occasionally appear in human hair, according to the University of South Carolina. The medulla does not have a well-defined appearance in human hair. This region of the hair consists of a central core of cells. The cortex consists of elongated, spindle-shaped cells. This region composes the main body of the hair.
Growth Cycle
The hair growth cycle consists of the anagen, catagen and telogen phases. The anagen phase results in a period of hair growth. After the anagen phase, the catagen phase occurs. This phase results in the degradation of the hair follicles. The catagen phase is followed by a period of rest called the telogen phase. Once this growth cycle ends, a period of shedding occurs before a new cycle begins.
Time Frame
Each phase in the hair growth cycle has a specific time frame. The anagen phase results in a growth period of approximately two to eight years, according to the International Society of Hair Restoration Surgery. The catagen phase lasts two to four weeks before the telogen phase begins. The telogen phase lasts two to four months.
Effects
The hair growth cycle results in continuous growth and shedding of hair from the scalp. The American Academy of Family Physicians (AAFP) reports that hair grows approximately 1cm per month during the anagen phase. The AAFP also reports that 90 percent of the hair on your scalp grows during any one time, while 10 percent of the hair is in a resting phase at any one time.
Problems
Normal hair loss results in the shedding of 50 to 100 hairs per day, according to the International Society of Hair Restoration Surgery. Excessive hair loss occurs for several reasons. Medical causes of hair loss include autoimmune diseases, thyroid disorders, hormonal problems, scalp infections and certain medications. Harsh styling techniques, such as corn rows and brads, also lead to hair loss. Discuss excessive hair loss with your doctor to determine the cause and develop an effective treatment plan.
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