length retention

Hair 101: Hair follicles and their life cycle

We are born with roughly 100,000 follicles on our scalp. We cannot regrow or generate new follicles after birth so what we are born with is what we have. Follicles create hair from stem cells that sit near the follicle and produce a new hair bulb (the white part located at the root end of a shed hair and is released with the hair). Over time, we lose follicles through factors such as age, hormone, or genetic follicular miniaturization or scarring disorders that destroy the abovementioned stem cells.

Blondes have roughly 20% more follicles than brunettes and redheads have about 20% fewer follicles. Asians and African Americans have fewer follicles and lower hair density than Caucasians. The follicles on the scalps of Caucasians and Asians are straight. The follicles curl and are on a greater angle on African American scalps. This curled follicle is the reason follicles are more difficult to harvest for hair transplants in African American patients.

Follicles cycle through three natural cycles, a growth phase, a rest phase, and a fall out phase, medically referred to as anagen, catagen, and telogen phases, respectively.  Each follicle individually cycles through these three phases independently of each other. Of those ~100 000 follicles, 85-90% are in anagen, <1% are in catagen, and 10-15% are in the natural fall out phase, telogen.  Follicles stay in the anagen growth phase for 2-6 years, catagen for 2-3 weeks, and telogen for 3 months before the hair is released from the follicle. Applying these numbers, you will shed  on average 100-200 hairs/day.  If these hairs are collected, it can appear as a large amount of hair but be reassured that a fresh new anagen hair helps to push out that old telogen hair and a new follicle cycle begins.

Anagen follicles grow scalp hairs at a rate of 0.35cm/day or roughly 1cm/month. This rate may increase with medications or pregnancy and decrease with age, nutrition, medications, and illnesses. Follicles only create hair in anagen growth phases.  Therefore, hairs only grow in anagen phase, so follicles in the catagen and telogen phase only rest and fall out, respectively.  The maximum length is greatest at the end of anagen phase with the exception of breakage which can shorten hairs. Proper hair care can help maintain length retention. Moisture regimens can be found at http://www.DrHillHairLoss.com/?p=73.

Check back to future installments of hair 101.

DrHillHairLoss

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