When hair appears to stop growing, the cause is rarely that the hair follicle has ceased function; the process is being interrupted. Hair growth is cyclical, where follicles repeatedly enter periods of growth, rest, and shedding. The perception of “stunted growth” results from two primary mechanisms: either the hair’s natural growth phase is prematurely shortened, or the hair shaft is breaking off at the rate it emerges from the scalp. Understanding the distinction between a biological halt and physical breakage is the first step in addressing the problem.
The Biological Limits of Hair Growth
The maximum length a person’s hair can achieve is fundamentally dictated by the duration of the hair growth cycle, which varies significantly from person to person. This cycle is divided into three main phases: anagen, catagen, and telogen. The anagen, or active growth, phase is the most important for length, as it is when cells in the hair bulb rapidly divide to form the hair shaft.
The anagen phase typically lasts between two and seven years, and the length of this phase is genetically predetermined for each individual. On average, hair grows about half an inch per month, meaning a shorter anagen phase places a natural cap on the terminal length, regardless of how well the hair is cared for.
Following the active growth is the catagen phase, a short transitional period lasting only a few weeks, where the hair follicle shrinks and detaches from the blood supply. The final stage, the telogen phase, is a resting period that lasts a few months before the old hair is shed and the follicle re-enters the anagen phase to begin growing a new hair. When the cycle is stable, roughly 90% of scalp hairs are in the anagen phase at any given time, but various factors can trigger a premature shift into the telogen phase, leading to noticeable shedding and a subsequent reduction in overall hair density.
Internal Health Conditions That Halt Growth
Systemic issues originating within the body are common causes of a shortened anagen phase or an abrupt shift into the telogen resting phase. Hormonal imbalances, for instance, are significant modulators of the hair cycle. Both an underactive (hypothyroidism) and an overactive thyroid gland (hyperthyroidism) can disrupt the normal cycle, often leading to diffuse hair thinning across the scalp.
Fluctuations in estrogen and progesterone, such as those experienced postpartum or during perimenopause, can trigger a temporary, synchronized shedding known as telogen effluvium. Conditions like Polycystic Ovary Syndrome (PCOS) can cause an excess of androgens, leading to a pattern of hair thinning. The stress hormone cortisol plays a direct role, as chronic, unmanaged stress elevates cortisol levels, signaling hair follicles to prematurely enter the resting and shedding phases. Noticeable hair loss typically occurs about three months after the stressful event.
The body prioritizes nutrient delivery to vital organs, making hair a non-essential structure that suffers quickly from deficiencies. Low iron levels, particularly ferritin stores, are a common deficiency linked to hair shedding, as iron is necessary for producing hair cell proteins. Inadequate levels of Vitamin D and Zinc can impair hair follicle function, interrupting the growth cycle and slowing new hair formation. Since hair is primarily composed of the protein keratin, insufficient protein intake weakens the hair structure and limits the necessary building blocks for growth.
External Factors Causing Breakage and Stagnation
In many cases, the hair is growing at a normal rate from the root, but the ends are breaking off just as quickly, resulting in the perception of stagnation. This is almost always caused by physical, chemical, or thermal damage to the hair shaft itself, which compromises the hair’s structural integrity. Chemical processes like frequent bleaching, perming, or permanent straightening treatments degrade the hair’s protein structure, making the strands porous and brittle.
High-heat styling tools used without adequate heat protection essentially boil the water inside the hair shaft, creating bubbles that weaken the cuticle and cortex. This thermal damage causes dryness and increases the likelihood of fracture. Mechanical stress from tight hairstyles, aggressive brushing, or friction from rough fabrics can cause trauma to the hair shaft, leading to breakage that prevents the hair from reaching its intended length.
When the outer layer of the hair, the cuticle, is damaged, the inner cortex loses moisture rapidly, leading to brittleness and the formation of split ends. Split ends, if not trimmed, can travel up the hair shaft, causing more extensive damage and breakage higher up the strand. Environmental factors, including UV radiation and air pollution, can cause oxidative stress that breaks down hair proteins, contributing to fragility and perceived lack of growth.
When To Consult a Specialist
If hair thinning or a perceived halt in growth is sudden, rapid, or accompanied by other noticeable symptoms, professional medical investigation is warranted. Shedding that lasts longer than six months may indicate a chronic form of telogen effluvium or another underlying condition. Visible patches of hair loss, widening of the part, or a receding hairline require evaluation, as they may signal specific types of alopecia.
Symptoms like unexplained fatigue, rapid weight changes, severe scalp itching, or inflammation suggest an internal health problem, such as a thyroid disorder or a nutrient deficiency, that must be addressed medically. If attempts to improve hair growth with over-the-counter treatments and changes to hair care routines fail to yield any improvement, consulting a dermatologist or trichologist is the most effective next step for an accurate diagnosis.