How Fast Does the Human Hair Grow?

Human hair can grow at different rates, but an average rate does exist.

Human beings are covered by millions of hairs from head to toe, hairs that are constantly growing. The answer to how fast the hair grows, however, varies depending on diet, age, genetics and general health.

Hair Structure

Keratin, a special protein also found in fingernails and toenails, composes the make up of human hair. A single hair is made of three layers: the cuticle, the outer layer which protects the inner two; the cortex, which contains melanin, the protein that determines hair color; and the medulla, which reflects light to give hair its color and tone.

Hair Growth Cycle

The first phase is the anagen phase, where the hair grows inside the follicle until it pushes through the dermis (skin). This phase can last between two to eight years. Next, hairs enter the catagen phase, a short phase of about two weeks, where the follicle shrinks and hair growth ceases. The third and final stage is the telogen phase, where the follicle rests for two to four months until the old hair falls out and the follicle begins again at the anagen phase.

Growth Rate

Human hair averages half an inch, or a little over one centimeter, per month of growth. This statistic fluctuates as hair near the crown and vertex of the head grow the fastest, while hairs in the temporal or beard areas grow slower. Also, people with thyroid problems may experience more rapid or slower growth, and those with hormone fluctuations, such as pregnant women, will also witness alterations in speed.

References

• Hair-Loss Help: How Does Hair Grow?
• Wise Geek.com: How Fast Does Human Hair Grow?
• Suite101.com: How Fast Does Human Hair Grow?