phase stretches for about two or three weeks, affecting about 1 to 2 percent of hair every day.
The HF cycle can typically be divided into three phases: anagen, catagen
, and telogen .
During the catagen
phase, cells of the germinal matrix undergo apoptosis; stem cells of the bulge migrate out of it to the external hair follicle, and subsequently, at the end of the catagen
phase, they form a new bulge around the hair stem and a new germinal matrix under the bulge.
in terminal scalp hair), regression (catagen
, I-VIII, 2-3 weeks in
Hair follicles normally regenerate, beginning with the rapidly growing anagen phase, transforming through the catagen
phase and resting at the telogen phase .
Hair follicles undergo a cycle of growing (anagen), regressing (catagen
), and resting (telogen) phases [1, 2].
The HF is a sac or a structure in the skin, which produces hair through a three-phase growth cycle as follows: anagen, catagen
, and telogen .
Li et al., "Identification of microRNAs in wool follicles during anagen, catagen
, and telogen phases in tibetan sheep," PLoS ONE, vol.
As the eyelash follicle enters the second or transitional stage (catagen
), which lasts approximately two weeks, it begins to shrink and hair growth ceases.
After the end of pregnancy the follicles in which anagen has been prolonged rapidly enters catagen
followed by telogen leading to telogen effluvium, which is evident for 6-16 weeks.
To produce new hairs, existing follicles undergo a process which has been defined for the mammalian hair cycle and consists of three phases: anagen, catagen
, and telogen 11].