Hair follicles grow in repeated cycles. One cycle can be
broken down into three phases.
1) Anagen - Growth Phase - Approximately
85 percent of the hair on your head is in the growing phase
at any given time. This phase can last 2 to 6 years. Hair
can grow at the rate of approximately 5 inches per year
and any individual hair is unlikely to grow more than one
2) Catagen - Transitional phase. When
the Anagen growth phase comes to an end, hair enters into
a Catagen phase which lasts about one or two weeks. During
this transitional phase, the hair follicle shrinks to about
1/6th of the normal diameter. The "root" is diminished
and the dermal papilla breaks away and rests below the scalp.
3) Telogen - Resting Phase. After the
catagen phase, hair goes into a resting phase known as telogen.
This period can last five to six weeks. Although the hair
does not grow during this stage, the dermal papilla stays
in the resting phase below the scalp. Approximately 10 to
15 percent of all hairs on your head are in this resting
phase at any given moment. At the end of this stage, the
hair follicle re-enters the growth phase. The dermal papilla
and the base of the follicle join together again and a new
hair begins to form. In some cases, the new hair will push
the old hair out of the way and the hair growth cycle starts
all over again.
Hair does not go through the hair growth cycle in patches
or patterns. Each hair can be in a different stage of this
cycle compared to the adjacent hairs.