(Hair Loss; Baldness)

ByWendy S. Levinbook, MD, Hartford Dermatology Associates
Reviewed/Revised Apr 2024
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Alopecia is defined as loss of hair from the body. Hair loss is often a cause of great concern to the patient for cosmetic and psychological reasons, but it can also be an important sign of systemic disease.

(See also Alopecia Areata.)

Pathophysiology of Alopecia

Growth cycle

Hair grows in cycles. Each cycle consists of phases:

  • Anagen: A long (2- to 6-year) growing phase

  • Catagen: A brief (3-week) transitional apoptotic phase

  • Telogen: A short (2- to 3-month) resting phase

At the end of the resting phase, the hair falls out (exogen). Normally, about 50 to 100 scalp hairs reach the end of resting phase each day and fall out. When a new hair starts growing in the follicle, the cycle begins again.

Disorders of the growth cycle include

  • Anagen effluvium—a disruption of the growing phase causing abnormal loss of anagen hairs

  • Telogen effluvium—significantly more than 100 hairs/day going into resting phase


Alopecia can be classified as focal or diffuse and by the presence or absence of scarring.

Scarring alopecia is the result of active destruction of the hair follicle. The follicle is irreparably damaged and replaced by fibrotic tissue. Several hair disorders show a biphasic pattern in which nonscarring alopecia occurs early in the course of the disease, and then scarring alopecia and permanent hair loss occurs as the disease progresses. Scarring alopecias can be subdivided further into primary forms, where the target of inflammation is the follicle itself, and secondary forms, where the follicle is destroyed as a result of nonspecific inflammation (see table Some Causes of Alopecia).

Nonscarring alopecia results from processes that reduce or slow hair growth without irreparably damaging the hair follicle. Disorders that primarily affect the hair shaft (trichodystrophies) also are considered nonscarring alopecia.


Etiology of Alopecia

The alopecias comprise a large group of disorders with multiple and varying etiologies (see table Some Causes of Alopecia).

Hair Loss Myths

The most common cause of alopecia is

  • Androgenetic alopecia (male-pattern or female-pattern hair loss)

Androgenetic alopecia is an androgen-dependent hereditary disorder in which dihydrotestosterone plays a major role. The prevalence of this form of alopecia increases with age, and it can affect over 70% of men (male-pattern hair loss) and 57% of all women (female-pattern hair loss) over the age of 80 (1, 2). However, prevalence rates vary among different populations.

Androgenetic Alopecia
Hide Details
This image shows androgenetic alopecia (male-pattern baldness).

Other common causes of hair loss are

  • Medications (including chemotherapeutic agents)

  • Infection (eg, tinea capitis, kerion)

  • Systemic disorders (eg, disorders that cause high fever, endocrine disorders)

  • Alopecia areata

  • Trauma

Traumatic causes include trichotillomania, traction alopecia, burns, radiation, and pressure-induced (eg, postoperative) hair loss.

Less common causes are

  • Primary hair shaft abnormalities

  • Autoimmune diseases

  • Lichen planopilaris/frontal fibrosing alopecia

  • Rare dermatologic conditions (eg, dissecting cellulitis of the scalp)

Etiology references

  1. 1. Adil A, Godwin M: The effectiveness of treatments for androgenetic alopecia: A systematic review and meta-analysis. J Am Acad Dermatol 77(1):136–141.e5, 2017. doi: 10.1016/j.jaad.2017.02.054

  2. 2. Gan DC, Sinclair RD: Prevalence of male and female pattern hair loss in Maryborough. J Investig Dermatol Symp Proc 10(3):184-189, 2005. doi: 10.1111/j.1087-0024.2005.10102.x

Evaluation of Alopecia


History of present illness should cover the onset and duration of hair loss, whether hair shedding is increased, and whether hair loss is generalized or localized. Associated symptoms such as pruritus and scaling should be noted. Patients should be asked about typical hair care practices, including use of braids, rollers, and hair dryers, and whether they routinely pull or twist their hair.

Review of systems should include recent exposures to noxious stimuli (eg, medications, illicit drugs, toxins, radiation) and stressors (eg, surgery, chronic illness, fever, psychological stressors). Symptoms of possible causes (eg, fatigue and hot or cold intolerance [hypothyroidism/hyperthyroidism] and, in women, hirsutism, deepening of the voice, and increased libido [virilization]) should be sought. Other features, including dramatic weight loss, dietary practices (including various restrictive diets), and obsessive-compulsive behavior, should be noted. In women, a hormonal/gynecologic/obstetric history should be obtained.

Past medical history should note known possible causes of hair loss, including endocrine and skin disorders. Current and recent medication use should be reviewed for offending agents (see table Some Causes of Alopecia). A family history of hair loss should be recorded.

Physical examination

Examination of the scalp should note the distribution of hair loss, the presence and characteristics of any skin lesions, and whether there is scarring. Part widths should be measured. Abnormalities of the hair shafts should be noted.

A full skin examination should be done to evaluate hair loss elsewhere on the body (eg, eyebrows, eyelashes, arms, legs), rashes that may be associated with certain types of alopecia (eg, discoid lupus lesions, signs of secondary syphilis or of other bacterial or fungal infections), and signs of virilization in women (eg, hirsutism, acne, deepening voice, clitoromegaly). Signs of potential underlying systemic disorders should be sought, and a thyroid examination should be done.

Red flags

The following findings are of particular concern:

  • Virilization in women

  • Signs of systemic illness or constellations of nonspecific findings possibly indicating poisoning

Interpretation of findings

Hair loss that begins at the temples and/or crown (vertex) and spreads to diffuse thinning or nearly complete hair loss is typical of male-pattern hair loss. Hair thinning on the crown manifesting as widening of the central part is typical of female-pattern hair loss (see figure Male- and Female-Pattern Hair Loss). In women, this is characterized by a central part width that is wider on the crown of the scalp than it is on the occipital scalp.

Male- and Female-Pattern Hair Loss (Androgenetic Alopecia)

Hair loss that occurs 2 to 4 weeks after chemotherapy or radiation therapy (anagen effluvium) can typically be ascribed to those causes. Hair loss that occurs 3 to 4 months after a major stressor (pregnancy, major febrile illness, surgery, medication change, or severe psychological stressor) suggests a diagnosis of telogen effluvium.

Other findings help suggest alternative diagnoses (see table Interpreting Physical Findings in Alopecia).

Manifestations of Hair Loss
Chemotherapy-Induced Anagen Effluvium
Chemotherapy-Induced Anagen Effluvium

    Anagen effluvium is a physiologic disruption of the anagen (growing) phase. It typically occurs several weeks after chemotherapy or radiation therapy. This photo shows an abrupt loss of hairs in the anagen phase along with sparse broken anagen hairs.

... read more

© Springer Science+Business Media

Acne Keloidalis Nuchae
Acne Keloidalis Nuchae

    This photo shows typical acneiform lesions and deep keloidal scarring alopecia in a young male with acne keloidalis nuchae.

... read more

© Springer Science+Business Media


    In this photo, the hair pulling is limited to the range of the person's right hand.

© Springer Science+Business Media

Other than hair loss, scalp symptoms (eg, itching, burning, tingling) are often absent and, when present, are not specific to any cause.

Signs of hair loss in patterns other than those described above are nondiagnostic and may require microscopic hair examination or scalp biopsy for definitive diagnosis.


Evaluation for causative disorders (eg, endocrinologic, autoimmune, toxic) should be done based on clinical suspicion.

Male-pattern hair loss usually requires no testing. When it occurs in young men with no family history, the physician should question the patient about use of anabolic steroids and other drugs. In addition to questions regarding prescription medication and illicit drug use, women with significant hair loss and abnormal menses, acne, hirsutism, or other evidence of virilization should have levels of appropriate hormones (eg, testosterone and dehydroepiandrosterone sulfate [DHEAS]) measured (see Hirsutism). Other laboratory testing in women with suspected androgenetic alopecia can include iron, ferritin, vitamin D, and thyroid function testing if indicated by history.

The pull test helps evaluate diffuse scalp hair loss. Gentle traction is exerted on a bunch of hairs (about 40) on at least 3 different areas of the scalp, and the number of extracted hairs is then counted. Normally, < 3 telogen-phase hairs should come out with each pull. If > 4 to 6 hairs come out with each pull, the pull test is positive and is suggestive of telogen effluvium.

Scalp biopsy is indicated when alopecia persists and diagnosis is in doubt. A 4-mm punch biopsy sectioned horizontally is preferred. Biopsy differentiates scarring from nonscarring forms. In cases of suspected cicatricial alopecia, specimens should be taken from areas of active inflammation, typically at the border of a bald patch. Noncicatricial alopecia should be sampled where hair is most sparse, typically in the center of the lesion. Fungal and bacterial cultures may be useful.

Daily hair counts can be done by the patient to quantify hair loss when the pull test is negative. Hairs lost during the first morning combing or during washing are collected in clear plastic bags daily for 14 days. The number of hairs in each bag is then recorded. Scalp hair counts of > 100/day are abnormal except after shampooing, when hair counts of up to 250 may be normal. Hairs may be brought in by the patient for microscopic examination.

Treatment of Alopecia

  • Medications (including hormonal modulators)

  • Laser light therapy

  • Surgery

Androgenetic alopecia

1alopecia areata and telogen effluvium. Hair regrowth can take 8 to 12 months. Treatment is continued indefinitely because, once treatment is stopped, hair loss resumes. The most frequent adverse effects are mild scalp irritation, allergic contact dermatitis2, 3).

inhibits the 5-alpha-reductase enzyme, blocking conversion of testosteroneMale Sexual Dysfunction); hypersensitivity reactions; gynecomastia; myopathy; and rarely symptoms of depression and suicidal ideation (4). There may be a decrease in prostate-specific antigen (PSA)

a medication used to treat benign prostatic hyperplasia3).

Hormonal modulators5–7).

Low-level laser light therapy is an alternate or additional treatment for androgenetic alopecia that has been shown to promote hair growth (8). Physician-dispensed and over-the-counter devices are available.

Autologous platelet-rich plasma injected into the scalp is thought to contain growth factors that promote hair follicle growth and maintenance (9).

Surgical options include follicle transplant, scalp flaps, and alopecia reduction. Few procedures have been subjected to scientific scrutiny, but patients who are self-conscious about their hair loss may consider them (7).

Hair loss due to other causes

Underlying disorders are treated.

Treatment for traction alopecia is elimination of physical traction or stress to the scalp.

Treatment for tinea capitis is oral antifungals.

Trichotillomaniaselective serotonin reuptake inhibitor

10, 11) or oral immunosuppressants (10, 1210, 13, 1415).

Hair loss due to chemotherapy (anagen effluvium) is temporary and is best treated with a wig; when hair regrows, it may be different in color and texture from the original hair. Hair loss due to telogen effluvium is usually temporary as well and abates after the precipitating agent is eliminated.

Treatment references

  1. 1. Olsen EA, Dunlap FE, Funicella T, et alJ Am Acad Dermatol 47(3):377-385, 2002. doi: 10.1067/mjd.2002.124088

  2. 2. Randolph M, Tosti AJ Am Acad Dermatol 84(3):737–746, 2021. doi: 10.1016/j.jaad.2020.06.1009

  3. 3. Gupta AK, Venkataraman M, Talukder M, Bamimore MAJAMA Dermatol 158(3):266–274, 2022. doi: 10.1001/jamadermatol.2021.5743

  4. 4. Nguyen D-D, Marchese M, Cone EB, et alJAMA Dermatol 157(1):35-42, 2021. doi:10.1001/jamadermatol.2020.3385

  5. 5. Sinclair R, Wewerinke M, Jolley D: Treatment of female pattern hair loss with oral antiandrogens. Br J Dermatol 152(3):466-73, 2005. doi: 10.1111/j.1365-2133.2005.06218.x

  6. 6. Famenini S, Slaught C, Duan L, et alJ Am Acad Dermatol 73(4):705-6, 201570. doi: 10.1016/j.jaad.2015.06.063

  7. 7. Adil A, Godwin M. The effectiveness of treatments for androgenetic alopecia: A systematic review and meta-analysis. J Am Acad Dermatol 77(1):136-141.e5, 2017. doi: 10.1016/j.jaad.2017.02.054

  8. 8. Jimenez JJ, Wikramanayake TC, Bergfeld W, et al: Efficacy and safety of a low-level laser device in the treatment of male and female pattern hair loss: A multicenter, randomized, sham device-controlled, double-blind study. Am J Clin Dermatol 15(2):115-27, 2014. doi: 10.1007/s40257-013-0060-6

  9. 9. Hesseler MJ, Shyam N: Platelet-rich plasma and its utilities in alopecia: A systematic review. Dermatol Surg 46(1):93–102, 2020. doi: 10.1097/DSS.0000000000001965

  10. 10. Ezemma O, Devjani S, Kelley KJ, et al: Treatment modalities for lymphocytic and neutrophilic scarring alopecia. J Am Acad Dermatol 89(2S):S33-S35, 2023. doi: 10.1016/j.jaad.2023.04.023

  11. 11. Abduelmula A, Sood S, Mufti A, et al: Management of cutaneous lupus erythematosus with Janus kinase inhibitor therapy: An evidence-based review. J Am Acad Dermatol 89(1):130-131. doi: 10.1016/j.jaad.2022.12.037

  12. 12. Fechine COC, Valente NYS, Romiti R: Lichen planopilaris and frontal fibrosing alopecia: Review and update of diagnostic and therapeutic features. An Bras Dermatol 97(3):348-357, 2022. doi: 10.1016/j.abd.2021.08.008

  13. 13. Ho A, Shapiro J: Medical therapy for frontal fibrosing alopecia: A review and clinical approach. J Am Acad Dermatol 81(2):568-580, 2019. doi: 10.1016/j.jaad.2019.03.079

  14. 14. Pindado-Ortega C, Saceda-Corralo D, Moreno-Arrones, et alJ Am Acad Dermatol 84(5):1285-1294, 2021. doi: 10.1016/j.jaad.2020.09.093

  15. 15. Verdelli A, Corrà A, Mariotti EB, et al: An update on the management of refractory cutaneous lupus erythematosus. Front Med (Lausanne) 9:941003, 2022. doi: 10.3389/fmed.2022.941003

Key Points

  • Androgenetic alopecia (male-pattern and female-pattern hair loss) is the most common type of hair loss.

  • Concomitant virilization in women should prompt a thorough evaluation for an underlying disorder.

  • Microscopic hair examination or scalp biopsy may be required for definitive diagnosis.

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