The belief that hair stops growing if it is not cut is a common misconception. The visible hair shaft above the skin is structurally dead and unconnected to the living cells that produce it. Hair growth is a continuous, cyclical process dictated by a biological clock deep within the scalp, independent of the hair’s length or whether the ends are trimmed. The idea that hair “stops growing” often arises when hair reaches a fixed maximum length, but this limit is pre-programmed by genetics and the natural lifecycle of each strand. Understanding this biology shows why cutting the ends does not influence growth at the root.
The Hair Growth Cycle
Hair production operates on a distinct, repeating cycle in the follicle beneath the skin, consisting of three main phases: anagen, catagen, and telogen. About 85% to 90% of the hairs on the head are actively growing in the anagen phase. The anagen phase is when cells in the hair root divide rapidly, causing the hair shaft to elongate. For scalp hair, this active period typically lasts between two and seven years, with hair growing at about half an inch per month. Once anagen ends, the hair enters the catagen phase, a brief transitional period lasting two to three weeks. During catagen, the hair follicle shrinks and detaches from its blood supply. The telogen phase, or resting phase, follows and lasts for approximately three months. The hair remains in the follicle but is not actively growing. After telogen, the old hair is shed and replaced by a new hair beginning the anagen phase, restarting the cycle.
The Role of Genetics in Maximum Length
The maximum length a person’s hair can achieve is determined primarily by the genetically predetermined duration of the anagen phase. Since hair grows roughly half an inch per month, the total time a hair is allowed to grow directly limits its potential length. For someone with a short anagen phase of only two years, their hair will reach a certain length before the growth cycle forces it to rest. Conversely, an individual with a longer anagen phase, lasting five to seven years, has the genetic potential to grow significantly longer hair. This explains why some people can grow hair down to their waist, while others find their hair naturally stops at a shoulder-length maximum. This growth phase duration is an internal factor that cannot be influenced by external actions, such as cutting the hair.
Cutting vs. Breakage
The belief that cutting hair makes it grow faster is a misunderstanding of the difference between growth and length retention. Hair growth occurs at the follicle level and is unaffected by trimming the hair shaft above the skin. Cutting only removes the oldest, most weathered section of the hair. The ends of long hair are susceptible to damage from styling, heat, and environmental factors, leading to split ends. If split ends are not removed, the damage can travel up the hair shaft, causing the hair to break off higher up. This breakage makes the hair appear shorter, leading to the perception that growth has slowed or stopped. Regular trims remove this fragile, damaged material, preventing further breakage and allowing the hair to retain the length it naturally grows from the root.