The hair growth cycle occurs in a set pattern that varies by individual. This pattern is continuous throughout a person's life, barring illness or treatments that result in abnormal hair loss. Each individual hair follicle is on a different part of the hair growth cycle, but all follow a similar pattern in each phase of the cycle.
Types
The hair loss cycle covers three phases. The first phase is the anagen (growth) phase, the second phase is the catagen (resting) phase and the last phase is the telogen (shedding) phase. Each phase plays an important part in the hair loss and regrowth cycle.
Anagen Phase
In the anagen phase, the hair follicle produces new hair and lengthens existing hair. Blood vessels feed the hair strands from the root, nourishing the strands to encourage growth. According to the Hair Loss Expert website, this phase generally lasts four to five years, and 90 percent of hair is in this phase at a time.
Catagen Phase
During the catagen phase, also known as the resting phase, hair begins to break down at the follicle. The International Society of Hair Restoration Surgery calculates that the catagen phase lasts from two to four weeks on average.
Telogen Phase
The telogen phase of the hair loss cycle is when hair loss occurs. The degraded follicle from the catagen phase falls out. During the telogen phase, you shed anywhere from 50 to 100 hairs per day. This phase is short-lived, and occurs as new hairs come in, beginning the anagen phase. The telogen phase lasts roughly two to four months according to the International Society of Hair Restoration Surgery.
Benefits
Having each hair follicle in a different phase of the hair growth cycle results in staggered and continual hair loss for a very small percent of hair. If every hair was in the same phase at the same time, all your hair would fall out at once during the shedding phase.
Considerations
Several factors can cause problems with the hair growth cycle. Hormone levels, thyroid diseases, stress and skin disease can all interrupt the cycle, leading to increased or excessive hair loss. Medications and treatments such as chemotherapy can also result in hair loss.
Warning
The shedding phase is where most individuals start to notice problems with hair loss. Abnormal shedding is the loss of more than 150 strands of hair a day. Shedding 150 or more strands of hair a day causes thinning and eventually baldness in some individuals. Excessive shedding is a medical condition known as alopecia; it necessitates a trip to the doctor.
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