A hair follicle is a structure in the skin that anchors each hair and produces the hair shaft. Hair growth occurs in a repeating, programmed cycle. When a follicle “goes back to” growth, it transitions from a resting phase back into an active production phase. This cyclical activity means the timeline for a follicle’s return to growth can vary from days to many months, depending on its natural state or any disruption it has experienced.
The Natural Cycle of Hair Follicle Activity
Hair growth is regulated by a cycle consisting of three main phases. The anagen phase is the active growth period where cells divide rapidly to form the hair shaft. This phase is the longest, lasting anywhere from two to seven years for scalp hair.
The catagen phase is a short transitional period lasting about two to three weeks. During this time, the follicle shrinks, detaches from its blood supply, and signals the end of hair production. The hair then enters the telogen phase, or resting period, where the follicle is inactive before being shed.
The transition from telogen back into anagen is when a follicle returns to growth. About 85 to 90 percent of scalp hairs are typically in the anagen phase. The duration of these phases differs significantly across the body; the anagen phase for body hair is much shorter than for scalp hair, limiting its length.
Recovery Timeline After Physical Disruption
When hair is physically cut or removed, the recovery timeline depends on whether the follicle structure was affected. Shaving or trimming removes only the hair shaft above the skin, leaving the active follicle intact and continuing its anagen phase. Since the hair root is still producing cells, stubble is typically noticeable within 24 to 48 hours as the hair emerges.
Methods that remove the entire hair from the root, such as plucking, waxing, or epilation, force the follicle to restart the growth process. If the hair was removed during the anagen phase, it usually takes about three to six weeks for a new hair to grow long enough to be visible above the skin.
The regrowth timeline is influenced by the hair’s location and the consistency of the removal method. Regular waxing can sometimes weaken the follicle over time, leading to slower and finer regrowth.
Duration of Follicle Dormancy
The natural period of dormancy is the telogen phase, a necessary resting stage for the follicle to regenerate. On the scalp, this phase typically lasts for approximately two to four months before the follicle naturally re-enters the active anagen phase. The telogen phase ends when the old hair, known as a club hair, is shed, allowing the new hair to begin growing.
This natural dormancy can be significantly prolonged by systemic factors that trigger telogen effluvium, causing a large number of follicles to prematurely enter the resting phase. Major physiological stressors, such as severe illness, childbirth, surgery, or rapid weight loss, can cause this shift.
Nutritional deficiencies, including a lack of iron, zinc, or certain vitamins, can also disrupt the normal cycle and extend the resting period. Hormonal fluctuations, such as those related to thyroid disorders or postpartum changes, are also known to delay the transition back to growth. The follicle is not damaged but remains in a holding pattern, and it may take several months after the underlying cause is resolved for the hair to re-enter the anagen phase.
Causes of Permanent Follicle Inactivity
In some cases, the hair follicle does not return to growth because it has become permanently inactive or destroyed. The most common cause of permanent loss is miniaturization, the hallmark of androgenetic alopecia (pattern baldness). Under the influence of the hormone dihydrotestosterone (DHT), genetically sensitive follicles progressively shrink with each cycle.
This shrinkage causes the follicle to produce increasingly finer, shorter vellus hairs, eventually stopping production entirely. The follicle remains technically present but is too small to grow a substantial terminal hair.
A second mechanism for permanent inactivity is scarring alopecia (cicatricial alopecia), which involves inflammation that physically destroys the follicle’s stem cells and structure. The follicle is replaced by permanent scar tissue, which makes regeneration impossible. Once the follicular unit is destroyed, the regenerative capacity is lost, and growth will not return.