The perception that hair is not growing causes significant frustration. While hair may appear stuck at a certain length, the issue often stems from a lack of length retention rather than a complete cessation of growth. Hair follicles are biologically active, producing new fibers, but these fibers may be breaking off at the same rate they are being created. Understanding this requires looking at the biological processes influencing hair health and the physical environment.
Understanding the Hair Growth Cycle
Hair growth follows a predictable, recurring sequence of phases known as the hair cycle, divided into three main stages: Anagen, Catagen, and Telogen. The Anagen phase is the active growth period, where cells in the hair root divide rapidly, pushing the hair shaft outward at an average rate of about half an inch per month.
The duration of the Anagen phase is the most important determinant of the maximum length hair can naturally achieve. This growth phase typically lasts between two and seven years, a period largely controlled by genetics. Following this, the Catagen phase begins, a short transitional time of about two to three weeks where the hair follicle shrinks and detaches from the dermal papilla.
The hair then enters the Telogen phase, a resting period lasting approximately three to four months before the hair is naturally shed. At any given time, about 85-90% of a healthy scalp’s hair is in the Anagen phase. A disruption to this timing, such as a premature shift into the Telogen phase, leads to noticeable thinning and a perceived lack of growth.
Internal Factors Inhibiting Growth
Systemic issues within the body frequently signal the hair follicle to prematurely shorten its growth period. Nutritional deficiencies are common culprits. A lack of sufficient iron, stored as ferritin, is necessary for the production of hemoglobin, which transports oxygen to the hair follicle, and low levels can force hair into the resting phase.
The minerals zinc and vitamin D also play important roles in the health of the hair bulb. Zinc is required for protein synthesis and tissue growth, including the keratin that makes up the hair shaft. Vitamin D helps regulate the hair follicle cycle, and deficiency has been linked to hair thinning.
Hormonal shifts represent another category of internal factors that disrupt the cycle. Thyroid disorders, whether overactive or underactive, affect hair growth by influencing the metabolism of the follicle cells. Similarly, the sharp drop in estrogen and progesterone after childbirth often triggers a synchronized shift of follicles into the Telogen phase, resulting in postpartum hair shedding.
A sensitivity to androgens, such as dihydrotestosterone (DHT), causes Androgenetic Alopecia, or pattern baldness. In genetically susceptible individuals, DHT causes the hair follicle to miniaturize, producing progressively finer and shorter hairs. This process shortens the Anagen phase until the follicles stop producing viable hair altogether.
The body’s response to chronic or significant stress can also interrupt the growth cycle, a phenomenon known as Telogen Effluvium. Prolonged periods of elevated stress hormones, like cortisol, signal hair follicles to enter the resting phase prematurely. The noticeable shedding typically occurs two to three months after the initial stressful event.
Length Retention Versus Growth Stagnation
For many people who believe their hair is not growing, the issue is excessive breakage of the hair shaft rather than a biological cessation of growth. True hair growth originates from the follicle, but length retention depends on the physical strength and health of the hair fiber itself. If hair is growing an inch a month but breaking off an inch a month, the length appears stagnant.
Mechanical damage is one of the most common causes of this breakage, stemming from routine physical stress. Aggressive brushing, especially when hair is wet and vulnerable, can fracture the hair shaft. Wearing overly tight hairstyles, such as slicked-back ponytails or buns, can cause tension that leads to breakage along the hairline and mid-shaft.
Friction from the environment also contributes to physical damage over time. Sleeping on rough fabrics, such as standard cotton pillowcases, creates drag and abrasion. This friction causes the outermost protective layer of the hair, the cuticle, to lift and fray, resulting in split ends and dryness.
Chemical processes inflict damage by altering the hair’s internal structure. Treatments like chemical relaxers or perms break the hair’s internal disulfide bonds to permanently change the hair’s shape. This process compromises the integrity and strength of the hair fiber. Similarly, bleaching strips the hair of its natural pigment by oxidizing the hair shaft, which severely weakens the cuticle and cortex. This damage makes the hair porous, brittle, and highly susceptible to snapping off.
When to Seek Professional Diagnosis
While improving hair care routines can resolve many cases of slow hair growth, persistent or sudden changes warrant a professional medical evaluation. A dermatologist or trichologist should be consulted if hair loss begins suddenly, occurs in distinct patches, or is accompanied by symptoms like scalp itching, burning, or scaling. These symptoms can indicate a more serious underlying condition, such as an autoimmune disorder or scarring alopecia.
A medical provider will typically begin with a thorough examination, followed by blood work to identify systemic causes. Common blood tests include checks for ferritin and iron levels, thyroid function, and a hormonal panel to measure androgens. Identifying a specific deficiency or imbalance is the first step toward a targeted treatment plan.
For conditions like Androgenetic Alopecia that require clinical intervention, prescription treatments are available. Topical Minoxidil is an over-the-counter option that works by increasing blood flow to the hair follicles, stimulating and prolonging the growth phase. Prescription oral medications like Finasteride or Spironolactone work by blocking the effects of androgens, which helps prevent further follicle miniaturization.