The idea that hair simply stops growing at a certain age is a misconception. Hair follicles are dynamic entities that cycle through phases of growth, transition, and rest throughout a lifetime. The perceived “stopping” of hair growth is actually a slowing down of the growth cycle. This process begins subtly in early adulthood and progresses with age, resulting in diminished density and length.
The Hair Growth Cycle
Hair production is a continuous, asynchronous cycle involving distinct phases, which ensures that hair shedding does not occur all at once. The first and longest phase is the Anagen phase, the period of active growth where root cells divide rapidly to form the hair shaft. This active phase typically lasts between two and seven years, with 80 to 90% of scalp hairs in Anagen. Hair grows at a rate of roughly one to one-and-a-half centimeters per month, and the length of this phase determines maximum hair length.
Following the Anagen phase is the Catagen phase, a brief transitional period lasting only about one to three weeks. During Catagen, the hair follicle shrinks and detaches from the dermal papilla, the structure providing nourishment. Only about one percent of scalp hairs are in this regressive phase at any moment.
The final phase is the Telogen phase, a resting period lasting about three to four months, during which the hair remains in the follicle but no longer grows. This resting hair is eventually shed, either by being pushed out by a new Anagen hair or through normal brushing and washing. About 10 to 15% of scalp hairs are in the Telogen phase, accounting for the normal daily shedding of 50 to 100 hairs.
How Aging Alters Hair Growth
With increasing age, the hair cycle begins to change, leading to a noticeable reduction in hair volume and length. The most significant alteration is the progressive shortening of the Anagen phase. As the growth phase decreases from several years to potentially just a few months, the hair does not have enough time to reach its previous maximum length before the strand is shed.
This shortening of the growth period is often accompanied by an increase in the proportion of follicles entering the Telogen, or resting, phase. A greater number of follicles in the resting state means fewer hairs are actively growing, leading to an overall decrease in hair density across the scalp. This shift in the cycle’s balance is a primary mechanism behind universal, age-related thinning.
Another fundamental change is follicle miniaturization, where the hair follicle gradually shrinks over successive cycles. Instead of producing a thick, pigmented terminal hair, the follicle generates increasingly finer, shorter, and less pigmented vellus-like hairs. This decrease in the hair strand’s diameter makes the hair feel softer and less dense. This contributes to the perceived loss of volume and makes the hair physically weaker.
Differentiating Normal Thinning from Pattern Baldness
It is important to distinguish between the universal, gradual thinning due to normal aging and the more pronounced condition known as Androgenetic Alopecia (AGA), or pattern baldness. Normal age-related thinning, sometimes termed senescent alopecia, is a diffuse reduction in hair diameter and density that affects the entire scalp. This thinning is a non-hormonal consequence of the natural aging process, where the hair cycles simply slow down for all follicles.
Androgenetic Alopecia is a genetically determined condition marked by a heightened sensitivity to the hormone dihydrotestosterone (DHT). The miniaturization in pattern baldness is accelerated and follows specific, predictable patterns. In men, this includes a receding hairline and thinning at the crown. For women, it typically manifests as diffuse thinning over the top of the scalp with a widening of the part, though the frontal hairline often remains intact. This type of hair loss is not exclusive to advanced age, as it can begin as early as the late teens or twenties for those with a genetic predisposition.