Last updated: August 15, 2021

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Alopecia is the loss of hair from any hair-bearing area of the body, but most often the scalp. It may be congenital or acquired, circumscribed or diffuse, and cicatricial or nonscarring. Androgenetic alopecia, a type of diffuse, nonscarring, acquired alopecia, is the most common, affecting > 70% of the general population by 70 years of age. Alopecia areata, an acquired, circumscribed, nonscarring alopecia, is the next most common type. Clinical diagnosis is usually possible. In ambiguous cases, diagnosis is aided by microscopic examination of the hair, trichograms, and scalp biopsy. Treatment depends on the type of alopecia and includes long-term (at least 1 year) use of topical minoxidil, corticosteroids (topical, intralesional, or oral), or antiandrogens. Surgery (hair transplant) or camouflaging techniques are used when medical therapy fails. The prognosis is variable and depends on the etiology and severity of hair loss.


Phases of hair growth

  • Anagen phase: phase of active growth
  • Telogen phase: resting phase
  • Catagen phase: phase of follicular regression


According to etiology (congenital/acquired) and pattern (diffuse/circumscribed)

Classification of alopecia according to etiology and pattern
Congenital Acquired

According to the presence of scarring

  • Cicatricial (scarring) alopecia
    • Brocq pseudopelade
      • Seen in women 30–55 years of age
      • Irregular areas of irreversible hair loss, which become scarred areas at a later stage
    • Lichen planopilaris
    • Frontal fibrosing alopecia (a progressive form of frontotemporal hair loss associated with local scarring)
    • Central centrifugal cicatricial alopecia
      • Alopecia that starts at the crown and spreads outwards
      • Occurs almost exclusively in black women > 50 years
    • Skin conditions causing scarring alopecia; : ichthyosis, dyskeratosis, discoid lupus erythematosus
    • Acquired scarring alopecia (e.g., via viral diseases, mycoses, burns, chemical burns)
  • Nonscarring alopecia


The diagnosis is often clear from the patient history and physical examination; however, there are several tests that allow confirmation of diagnosis.

  • Hair pull test: About 50 strands of hair are lightly tugged away from the scalp; if > 5 strands can be pulled out, the test is positive.
  • Dermoscopy: examination of the scalp skin, follicle size, and hair shaft diameter by magnification
  • Microscopic examination: performed on hair follicles and shaft to determine the phase of hair growth (anagen, telogen) and structural abnormalities of the shaft
  • Scalp biopsies (performed from sites of active disease): to confirm the diagnosis of cicatricial alopecia
  • Trichograms: aids diagnosis and prognosis of nonscarring alopecia


Congenital diffuse alopecia

  • Trichorrhexis nodosa: A hair shaft deformity characterized by the development of weak points in the shaft due to physical/chemical trauma in genetically predisposed individuals.
  • Pili torti: The hair shaft is flattened and has multiple twists which lead to fragile hair that breaks easily.
  • Monilethrix (beaded hair): Autosomal dominant disorder with beaded hair shafts which break easily, close to the scalp, a few months after birth.
  • Genetic syndromes: Menkes disease, Netherton's syndrome, etc.

Acquired diffuse alopecia

Androgenetic alopecia

Features and treatment of androgenetic alopecia in men and women
Men (male pattern baldness) Women (female pattern baldness)
Clinical features
  • Gradual, nonscarring hair loss
    • Bitemporal "M” pattern of recession
    • May be followed by hair loss on the vertex of the scalp
    • 10% of men have a female pattern of balding.
  • Follicular miniaturization is seen in the affected parts
  • First-line treatments
  • Hair transplant surgery: Follicular units from the occipital scalp are extracted (either as small units or as a linear strip), divided into small units, and implanted into the bald areas.
  • Camouflage: keratin fibers, hair dyes, toupées, etc.

Telogen effluvium

Anagen effluvium


Congenital circumscribed alopecia

  • Temporal triangular alopecia
    • A well-defined oval/triangular patch of alopecia in the temporal part of the scalp
    • Seen before 5 years of age
    • Mimics alopecia areata and is differentiated from it by the presence of vellus hair and the absence of exclamation point hair
    • Treatment (if necessary): hair transplant/surgical excision
  • Nevus sebaceus
  • Aplasia cutis congenita
    • Intra-uterine developmental disruption of one/more layers of the scalp
    • A part of the scalp is missing at birth, which, on healing, causes scarred, hairless patch
    • Treatment
      • Small lesions: no treatment
      • Large lesions: surgical excision + primary closure/repair (with help of tissue expanders and skin flaps)

Acquired circumscribed alopecia

Alopecia areata

Traction alopecia

  • Definition: Hair loss due to chronic traction/tension on the hair follicles, mostly at the frontal and temporal scalp
  • Etiology: Hairstyles involving tying the hair tightly
  • Treatment


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