Understanding Hair Growth and Hair Loss

How Hair Actually Grows

Most people think of hair loss as something that happens to hair. It is more accurate to think of it as something that happens to hair follicles, the structures beneath the scalp surface that produce hair. Understanding hair growth and hair loss at the follicle level makes everything else about causes, treatment, and what to expect significantly easier to understand.

Each hair follicle operates on its own independent cycle, moving through four phases continuously throughout your life. At any given moment, your follicles are at different points in this cycle, which is why healthy hair sheds and regrows constantly without producing visible thinning.

Anagen: The Growth Phase

The anagen phase is the active growth period. A hair in anagen is being produced continuously by the follicle, growing approximately half an inch per month. This phase typically lasts two to seven years, and its duration determines how long your hair can grow. People with very long hair simply have follicles with longer anagen phases. At any given time, approximately 85 to 90 percent of your scalp hairs are in anagen.

Catagen: The Transition Phase

Catagen is a brief transition lasting about two to three weeks. The follicle begins to shrink, detaches from its blood supply, and stops producing new hair. Only about one percent of hairs are in catagen at any time.

Telogen: The Resting Phase

During telogen, the hair remains in the follicle but no growth occurs. The follicle is at rest while a new hair begins forming beneath the old one. Telogen lasts approximately two to four months, and roughly ten to fifteen percent of hairs are typically in this phase at any given moment.

Exogen: The Shedding Phase

Exogen is the phase in which the old hair is released and shed as the new hair below it pushes through. Losing 50 to 100 hairs per day is entirely normal and reflects this ongoing cycle. The hairs you find on your pillow, in the shower drain, and in your brush are overwhelmingly hairs completing a natural cycle, not a sign of abnormal loss.

Hair loss occurs when this cycle is disrupted. If the anagen phase shortens, follicles spend less time growing and more time resting, producing finer, shorter hairs with each successive cycle. If follicles are damaged or destroyed, they stop cycling entirely. Understanding which disruption is occurring points directly to the cause and, therefore, to the appropriate treatment.

The Most Common Causes of Hair Loss

Hair loss has many possible causes, but one dominates: androgenetic alopecia, male and female pattern hair loss, accounts for the overwhelming majority of cases in both men and women. The other causes are meaningfully different in their biology, their presentation, and their treatment, which is why accurate identification matters before any treatment decision is made.

Androgenetic Alopecia: Pattern Hair Loss

Androgenetic alopecia is a genetic condition in which hair follicles are sensitive to dihydrotestosterone (DHT), a hormone derived from testosterone by the enzyme 5-alpha reductase. In genetically predisposed individuals, DHT binds to receptors in scalp follicles and causes them to progressively miniaturize. Each successive growth cycle produces a thinner, shorter hair until the follicle eventually becomes dormant.

In men, this typically follows a predictable progression: receding at the temples, thinning at the crown, eventually merging into more extensive loss mapped by the Norwood-Hamilton Scale. In women, the pattern is usually diffuse thinning across the crown and top of the scalp with the frontal hairline preserved, mapped by the Ludwig Scale. The rate of progression varies significantly between individuals.

Androgenetic alopecia is progressive and lifelong. It does not resolve on its own. Treatment slows or manages the progression. It does not cure the underlying genetic predisposition. The earlier treatment begins, the more follicles remain viable and the better the outcome. Learn more about androgenetic alopecia →

Telogen Effluvium: Stress-Related Shedding

Telogen effluvium occurs when a physical or emotional stress pushes a large number of follicles into the telogen (resting) phase simultaneously. Two to four months later when those follicles complete the cycle and shed a noticeable increase in hair loss appears. Common triggers include illness, surgery, rapid weight loss, childbirth, severe emotional stress, and nutritional deficiency.

The characteristic feature is diffuse shedding across the whole scalp rather than patterned thinning. It is typically temporary: once the trigger is removed or resolved, the follicles return to normal cycling and the hair regrows. Identifying and addressing the trigger, including nutritional deficiencies, is the primary treatment approach. Learn more about telogen effluvium →

Alopecia Areata: Autoimmune Hair Loss

Alopecia areata is an autoimmune condition in which the immune system mistakenly attacks hair follicles, causing sudden patchy hair loss. The patches are typically smooth and well-defined. In some cases the condition progresses to total scalp hair loss (alopecia totalis) or complete body hair loss (alopecia universalis).

Alopecia areata is unpredictable. It can resolve spontaneously or persist for years. Treatment options have expanded significantly in recent years with the FDA approval of JAK inhibitor medications specifically for this condition. Learn more about alopecia areata → | Learn more about alopecia totalis and universalis →

Traction Alopecia: Tension-Caused Hair Loss

Traction alopecia results from repeated mechanical stress on the hair follicle from tight hairstyles including braids, tight ponytails, buns, extensions, and weaves worn consistently over time. The follicles at the hairline and temples are most commonly affected. If caught early, traction alopecia is often reversible with changes to styling practice. Left untreated, the repeated trauma can permanently damage follicles and produce scarring. Learn more about traction alopecia →

Scarring Alopecia: Permanent Follicle Loss

Scarring alopecia is also called cicatricial alopecia. It refers to a group of conditions in which inflammation destroys hair follicles and replaces them with scar tissue. Because scarred follicles cannot regrow hair, the hair loss in affected areas is permanent. Early diagnosis and prompt treatment are critical to limiting the extent of permanent loss. Learn more about scarring alopecia →

Trichotillomania: Compulsive Hair Pulling

Trichotillomania is a psychological condition involving the compulsive urge to pull out one’s own hair from the scalp, eyebrows, or other areas. The resulting hair loss is irregular and patchy, distinguishable from other forms of alopecia by the broken hairs of varying lengths in affected areas. Effective treatment typically combines behavioral therapy with medical support. Learn more about trichotillomania →

Chemotherapy and Medical Treatment-Related Hair Loss

Certain medical treatments, particularly chemotherapy and radiation therapy targeting the head or neck, cause hair loss by affecting rapidly dividing cells, including those in hair follicles. This type of loss is usually temporary, with regrowth beginning after treatment concludes, though the timeline and extent of regrowth vary. Learn more about chemotherapy and medical hair loss →

Hormonal and Nutritional Contributing Factors

Beyond the primary diagnoses above, several factors can trigger or accelerate hair loss. Thyroid dysfunction, both hypothyroidism and hyperthyroidism, commonly causes diffuse shedding that typically improves with appropriate hormone management. Iron deficiency, particularly in women, is one of the most frequently overlooked contributors to hair loss and can produce significant shedding that responds well to correction. Vitamin D deficiency and zinc deficiency have also been linked to impaired hair growth. Rapid weight loss is a well-established trigger for telogen effluvium.

These factors rarely cause hair loss in isolation. They more commonly act as accelerants on an underlying predisposition or as triggers for temporary shedding episodes. Addressing them is an important part of any treatment program but is not a substitute for treating the primary condition.

H2: Recognizing the Early Signs

Different types of hair loss present differently, and recognizing the pattern is the first step toward understanding the cause.

Male pattern hair loss typically begins with recession at the temples forming an M-shape, followed by thinning at the crown. Female pattern hair loss typically presents as overall reduction in density across the top of the scalp, a widening part line, and increasing visibility of the scalp without a receding hairline.

Alopecia areata produces smooth, round or oval patches of sudden hair loss rather than gradual progressive thinning. Traction alopecia concentrates at the hairline and temples. Telogen effluvium produces diffuse shedding across the whole scalp, often noticed as increased hair on pillows, in the shower, and in the brush.

Changes in hair texture, thickness, and the length hair can achieve before appearing to stop growing are often earlier signals than visible thinning. The anagen phase shortening before the visual consequences become apparent.

Normal daily shedding of 50 to 100 hairs is part of the healthy cycle. A simple indicator of increased shedding is gently pulling a small section of hair. If more than two or three hairs release easily, it may warrant attention.

What to Do If You Are Noticing Hair Loss

The most useful action you can take when understanding hair growth and hair loss is to schedule a consultation with a qualified hair restoration specialist. Not because every hair loss situation requires intervention, but because the right response depends entirely on understanding what type of hair loss you are experiencing. The treatments that work for androgenetic alopecia are different from those for telogen effluvium, which are different again from those for alopecia areata. Starting with a treatment for the wrong condition wastes time and allows further loss to occur while the actual cause goes unaddressed.

A qualified specialist will assess your pattern of loss, take a history that includes relevant health factors, and help you understand what you are dealing with and what your options are. For androgenetic alopecia, by far the most common scenario, the full range of options includes medical treatments, device-based therapies, non-surgical hair replacement, and surgical restoration, used individually or in combination.

The consistent finding across all treatment approaches is that outcomes are better when treatment begins earlier. Follicles that are miniaturizing can often be preserved. Follicles that have been dormant or inactive for years generally cannot. The window to act is not indefinite.

Treatment Options Overview

A full discussion of each treatment is covered on our dedicated pages linked below. This is a brief orientation.

• Medical treatments: Minoxidil (topical, FDA-approved for both men and women) and finasteride (oral prescription, approved for men) are the two most established pharmaceutical treatments for androgenetic alopecia. Both require ongoing use to maintain results. Learn more about hair loss treatment and prevention →
• Low-level laser therapy (LLLT): An FDA-cleared non-surgical treatment using specific wavelengths of light to stimulate follicle activity, slow miniaturization, and improve hair density. Works best in the early to moderate stages of androgenetic alopecia and combines well with other treatments. Laser hair therapy for men → | Laser hair therapy for women →
• PRP therapy: Uses concentrated growth factors from your own blood to stimulate follicle health and reduce shedding. Administered in a series of in-office sessions. Effective for both men and women in the early to moderate stages of loss. PRP therapy for men → | PRP therapy for women →
• Scalp micropigmentation: A cosmetic procedure that deposits pigment into the scalp to replicate the appearance of hair follicles, adding visual density and definition. SMP is not a growth treatment. It is a cosmetic solution that provides immediate results. Learn more about scalp micropigmentation →
• Non-surgical hair replacement: Custom-designed hair systems that integrate with existing hair or provide full coverage. Immediate results with no recovery period. A complete solution for men and women at any stage of hair loss. Non-surgical replacement for men → | Non-surgical replacement for women →
• Hair transplant surgery: A permanent surgical procedure that relocates DHT-resistant follicles from donor areas into thinning or balding areas. The only treatment that delivers permanent results. Appropriate for men and women who meet candidacy criteria. Hair transplants for men → | Hair transplants for women →

Talk to a Hair Loss Specialist

Understanding your hair loss is the starting point. But the most useful next step in understanding hair growth and hair loss is a conversation with someone who can assess your specific situation and help you understand what options are right for you.

Transitions International members specialize exclusively in hair restoration. They work with both men and women across the full spectrum of hair loss types and treatment approaches from the earliest signs of thinning through advanced loss and they build individualized plans rather than recommending one-size-fits-all products or procedures. The earlier the conversation happens, the more can be done.