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Hair loss (medically called alopecia) is the partial or complete loss of hair from areas where it normally grows, most often the scalp. It ranges from gradual, patterned thinning to sudden, diffuse shedding, and it can be temporary or permanent depending on the underlying cause.
Hair loss is not a single disease but a sign shared by many different conditions. To understand it, it helps to understand the hair growth cycle. Each follicle moves through three phases: anagen (active growth, lasting years), catagen (a brief transition), and telogen (resting, after which the hair is shed). At any moment, roughly 85–90% of scalp follicles are in the growing phase and about 10–15% are resting (NIH/StatPearls). Because of this cycle, losing about 50–100 hairs per day is normal.
Hair loss becomes a medical concern when shedding outpaces regrowth, when follicles miniaturize (produce progressively finer, shorter hairs), or when follicles are destroyed. Dermatologists divide alopecia into two broad groups:
In ICD-10, common forms are coded under L63 (alopecia areata), L64 (androgenetic alopecia), and L65 (other non-scarring hair loss, including telogen effluvium).
The causes differ by type, and identifying the right one drives everything that follows.
This is by far the most common cause. It is driven by genetic susceptibility and the effect of androgens (particularly dihydrotestosterone, DHT) on genetically sensitive follicles, which gradually miniaturize. Prevalence rises steadily with age—affecting a large majority of men and roughly half of women by age 70 in studied populations (StatPearls). Men typically develop a receding hairline and crown thinning; women more often show diffuse thinning over the crown with a preserved frontal hairline.
A temporary, diffuse shedding that occurs when a physiologic stressor pushes an abnormally large share of follicles into the resting phase at once. Common triggers (DermNet, NIH) include childbirth, major surgery, high fever or severe illness, rapid weight loss or crash dieting, iron deficiency, thyroid disease, and certain medications. Shedding usually begins 2–3 months after the trigger.
An autoimmune condition in which the immune system attacks hair follicles, producing smooth, round patches of loss on the scalp or body. It can progress to total scalp loss (alopecia totalis) or whole-body loss (alopecia universalis). It is associated with other autoimmune conditions and a family history of the disorder (NIH/NIAMS).
Symptoms depend on the cause, and the *pattern* is often the most useful clue:
Warning signs of *scarring* loss include loss of the visible follicle openings (a smooth, shiny scalp), persistent burning or tenderness, and an irregular, advancing border.
Diagnosis begins with history and a close scalp examination. A clinician typically asks about timing, family history, recent illness or stressors, diet, medications, and hairstyling practices. Several in-office tests refine the picture:
Severity in androgenetic alopecia is often staged with the Hamilton-Norwood scale (men) or the Ludwig scale (women).
Treatment depends entirely on the cause, and the most important first step is an accurate diagnosis. The general approach moves from addressing reversible factors, to over-the-counter therapy, to prescription options.
Some hair loss resolves once the trigger is removed. Telogen effluvium is usually self-limited and regrows over 3–6 months once the precipitating illness, deficiency, or medication is corrected. Practical steps include treating iron deficiency or thyroid disease, ensuring adequate protein and overall nutrition, reviewing medications with a prescriber, and easing high-tension hairstyles to prevent traction alopecia. Gentle hair handling does not regrow hair on its own but limits avoidable breakage.
Not all hair loss is preventable—androgenetic alopecia and alopecia areata are driven by genetics and immune factors that cannot be willed away. But several measures genuinely help:
Most hair shedding is benign, but certain features deserve professional evaluation:
Scarring alopecias in particular are time-sensitive: once a follicle is destroyed, the loss is permanent, so early diagnosis is critical.
The outlook depends heavily on the type. Telogen effluvium is usually fully reversible, with regrowth over several months once the trigger resolves. Androgenetic alopecia is progressive without treatment, but therapy can slow or partly reverse it and is most effective when started early; results require ongoing maintenance. Alopecia areata is unpredictable—many people with limited patches regrow hair spontaneously, while extensive disease is harder to treat, though JAK inhibitors have meaningfully improved options for severe cases. Scarring alopecias carry the most guarded prognosis because destroyed follicles cannot regrow, making early intervention essential to preserve remaining hair. Across all types, hair loss is not life-threatening, and its substantial psychological impact is well recognized and treatable.
Is it normal to lose hair every day? Yes. Shedding roughly 50–100 hairs per day is a normal part of the hair cycle. Concern is warranted when you notice a clear increase, visible thinning or bald patches, or hair not regrowing.
Will my hair grow back? It depends on the cause. Telogen effluvium and many cases of alopecia areata regrow. Androgenetic alopecia can be slowed and partly reversed with treatment but tends to progress if untreated. Scarring alopecias generally do not regrow, which is why early evaluation matters.
Do over-the-counter supplements and "hair growth" vitamins work? They help only if you have a true deficiency, such as low iron. In people with normal nutrient levels, evidence that general supplements regrow hair is weak, and excess of some nutrients (for example, vitamin A or selenium) can actually cause hair loss.
Does stress cause hair loss? Severe physical or emotional stress can trigger telogen effluvium, a temporary diffuse shedding that begins a couple of months after the event. It typically reverses once the stressor passes. Stress is not the cause of androgenetic alopecia.
How long until I see results from treatment? Hair grows slowly, so most therapies require 3–6 months of consistent use before noticeable change, and ongoing use to maintain it. Some people experience a brief increase in shedding when starting minoxidil before improvement appears.
FDA-approved and evidence-based options depend on the cause. For androgenetic (pattern) hair loss: topical minoxidil (FDA-approved 1988; over-the-counter for men and women) and oral finasteride (FDA-approved 1997 for men only; not approved and contraindicated in women who are or may become pregnant). For severe alopecia areata (an autoimmune type), the FDA has approved three oral JAK inhibitors: baricitinib (Olumiant, 2022, adults), ritlecitinib (Litfulo, 2023, ages 12+), and deuruxolitinib (Leqselvi, 2024, adults). In the ALLEGRO trial, about 23% of patients on ritlecitinib 50 mg achieved 80%+ scalp coverage (SALT score of 20 or less) at six months versus 1.6% on placebo. Other clinician-directed measures include treating underlying conditions (e.g., thyroid disease, iron deficiency), corticosteroids for alopecia areata, low-level laser therapy, and hair transplantation. Off-label oral or low-dose minoxidil and oral finasteride/dutasteride are sometimes prescribed. JAK inhibitors and finasteride carry meaningful risks and require a prescription and medical supervision. This is general information, not medical advice; a board-certified dermatologist or your clinician can match treatment to your specific diagnosis.
Hair loss most commonly results from heredity, known as androgenetic alopecia (male- or female-pattern baldness), which accounts for the majority of cases. Other causes include hormonal changes (such as pregnancy, menopause, or thyroid problems), physical or emotional stress, certain medications, nutritional deficiencies like low iron, autoimmune conditions such as alopecia areata, and scalp infections. Because the underlying cause shapes treatment, a clinician or dermatologist should evaluate persistent or sudden hair loss to identify the type.
It depends on the cause. Temporary types like telogen effluvium (stress- or illness-related shedding) usually reverse on their own once the trigger resolves, with hair typically regrowing over several months. Hereditary pattern baldness cannot be fully cured or permanently reversed, but treatments such as minoxidil and finasteride can slow loss and partially regrow hair, especially when started early; once a follicle is scarred or has stopped producing hair, regrowth is not possible. A dermatologist can advise which outcome is realistic for your situation.
Losing up to about 100 hairs per day is generally considered normal, as hair naturally cycles through growth and shedding phases. Shedding noticeably more than this, finding clumps in the shower or on your pillow, or seeing visible thinning or bald patches can signal a problem. In telogen effluvium, daily shedding can rise to roughly 300 hairs. If you are concerned about the amount you are losing, see a healthcare provider for an assessment.
Early signs depend on the type but commonly include gradual thinning at the top of the scalp, a receding hairline, or a widening part. Other patterns include circular or patchy bald spots (often a sign of alopecia areata), sudden loosening or handfuls of hair coming out when washing or brushing, and full-body hair loss from some medical treatments. Scaling, redness, or broken hairs that look like black dots can point to a scalp infection. Noticing these changes early and consulting a clinician improves the chances that treatment will help.
See a doctor if you notice sudden or patchy hair loss, more shedding than usual, thinning patches on your scalp, or hair loss accompanied by itching, pain, redness, or scaling. Sudden loss can sometimes signal an underlying medical condition that needs treatment, and early evaluation gives the best chance of preserving or regrowing hair. A primary care provider or dermatologist can diagnose the type using a scalp exam, blood tests, a gentle hair-pull test, or occasionally a scalp biopsy.
A clinician diagnoses the cause through a medical history and physical exam of your scalp and hair, often supplemented by simple tests. These can include a hair-pull test (in telogen effluvium, gently tugging may release four or more hairs), blood tests to check for iron deficiency, thyroid dysfunction, or hormonal causes, and sometimes a scalp biopsy or microscopic examination of hairs. Because so many conditions cause hair loss, professional diagnosis is the most reliable way to choose an effective treatment rather than self-treating.
The main evidence-based treatments are topical minoxidil (available over the counter), which can slow loss and promote regrowth in both men and women, and oral finasteride, a prescription medication for men that blocks the hormone DHT. Other options include hair transplant surgery, platelet-rich plasma (PRP) injections, low-level laser therapy, and treating any underlying condition such as thyroid disease or iron deficiency. Medications generally take 3 to 6 months to show results and must be continued long term, since stopping usually leads to losing the regained hair. A dermatologist can recommend the right option based on the diagnosis.
Hereditary (pattern) hair loss cannot be fully prevented because it is genetically driven, but its progression can often be slowed, especially when treatment begins early. Starting medications like minoxidil or finasteride at the first signs may help preserve existing hair longer. You can also reduce other contributing factors by managing stress, eating a balanced diet with adequate protein and iron, and avoiding tight hairstyles or harsh treatments that cause traction or breakage. Discuss prevention strategies with a clinician, as approaches differ by individual.
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This page is for general information and is not medical advice. Always consult a qualified clinician about diagnosis and treatment. Individual results vary.