Final answer:
The anagen phase is the active stage of hair growth, where cells divide rapidly, pushing the hair shaft out. It lasts 2 to 7 years and is followed by the catagen and telogen phases, which represent transitional and resting periods, respectively.
Step-by-step explanation:
The stage of hair growth considered the active phase is known as the anagen phase. This is the period during which cells divide rapidly at the root, pushing the hair shaft up and out. The anagen phase is the longest duration of the hair growth cycle, typically lasting from 2 to 7 years. Hair grows at a rate of 0.3 mm per day during this phase, contributing to the overall length of the hair.
Following the anagen phase is the catagen phase, a transitional period that lasts about 2 to 3 weeks and marks the end of active hair growth. The telogen phase is the resting phase where no new growth occurs. This stage lasts 2 to 4 months before the cycle starts anew with the anagen phase. Hair loss becomes noticeable if shedding exceeds hair replacement, which may be due to factors such as hormonal or dietary changes, aging, or hormonal influences.