A normal head of hair contains about 120,000-150,000 strands of hair.

Usually, at any one time, about 90% of those hairs are in a growing phase, growing by about 1/2 inch each month.

This phase lasts for two to three years.  At that point, a hair will go into a resting stage. This "rest" lasts for 3 to 4 months before the hair falls out and is replaced by a new one.

"Typically, people shed about 100 hairs a day," says Carolyn Jacob, MD, founder and medical director of ChicagoCosmetic Surgery and Dermatology. "Most people don't even notice."

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