Hair growth is a biological process, often raising questions about whether it grows during sleep. Understanding its mechanisms clarifies this. Hair growth is not a process that pauses or accelerates with sleep; instead, it is a continuous activity driven by hair follicles. This constant production of hair fibers is part of an intricate cycle, operating independently of sleep.
The Constant Process of Hair Growth
Hair growth is a continuous process, occurring regardless of whether a person is awake or asleep. Each hair follows a distinct growth cycle, and individual follicles operate independently. This continuous nature ensures that not all hair falls out at once, maintaining a relatively stable hair density. The average rate of human scalp hair growth is about half an inch per month, or six inches per year.
The hair growth cycle consists of three primary phases: anagen, catagen, and telogen. The anagen phase is the active growth period, where cells in the hair root divide rapidly, forming new hair. This is the longest phase, lasting two to eight years for scalp hair, with 85% to 90% of scalp hairs in this phase. Hair length is directly influenced by the duration of this anagen phase.
Following the anagen phase is the catagen phase, a short transitional period lasting about two to three weeks. During this time, hair growth slows, and the hair follicle shrinks, detaching from its blood supply. About 3% of hairs are in this stage.
The final stage is the telogen phase, a resting period lasting two to three months. Hair remains in the follicle but is not actively growing; eventually, the old hair sheds to make way for new hair growth as the cycle restarts. 9% to 15% of scalp hairs are in this resting phase, and it is normal to shed between 50 to 100 hairs daily as part of this cycle.
How Sleep Supports Hair Health
While hair growth is a continuous process, the quality of sleep plays an indirect but important role in hair health. Sleep is when the body undergoes repair and regeneration, extending to hair follicles. Adequate sleep contributes to hormonal balance and stress reduction, creating an optimal environment for healthy hair.
During deep sleep stages, the body releases human growth hormone (HGH), which is involved in cell regeneration and tissue repair, including cells within hair follicles. This hormone production is prominent in the early hours of restorative sleep. Insufficient sleep can reduce HGH levels, which can lead to slower hair growth and weaker strands.
Sleep also influences the body’s stress response. Lack of sleep can elevate cortisol, a stress hormone. High cortisol can disrupt the hair growth cycle, pushing follicles into the resting (telogen) phase prematurely, leading to increased shedding. Melatonin, a sleep-regulating hormone, also plays a role in hair growth by synchronizing the hair cycle and extending the active growth phase. Consistent, quality sleep supports the body’s natural restorative functions, indirectly fostering a healthy environment for hair.