Version May 2024
| Epidemiology | Clinical features on scalp | Nonscalp involvement | Pathology | Hair pull test | |
| Focal hair loss | |||||
| Alopecia areata* | Onset most common in childhood or young adulthood | Round patches of nonscarring alopecia with exclamation point hairs; may extend to total hair loss on scalp (alopecia totalis) or loss of all body hair (alopecia universalis); uncommon is a diffuse hair loss presentation | Other hair-bearing sites may be affected, nail pitting, trachyonychia | Increased catagen/telogen hair follicles; peribulbar lymphocytic infiltrate resembling "swarm of bees" around anagen follicles in some cases; multiple miniaturized hair follicles; trichomalacia and pigment casts | Positive hair pull test, telogen hairs and dystrophic anagen hairs |
| Traction alopecia | Individuals with chronic use of traction-inducing hairstyles | Loss of terminal hairs in areas of traction; prolonged traction may lead to cicatricial alopecia | N/A | Acute: increased catagen/telogen hairs, occasional pigment casts Chronic: reduction in terminal hairs, occasional fibrous tracts, retained sebaceous glands | Normal or positive with broken hair fibers |
| Alopecia syphilitica | Most common in young adults; occurs due to secondary syphilis | Patchy hair loss, "moth-eaten" appearance | Other mucocutaneous manifestations of secondary syphilis | Increase in catagen/telogen follicles, perifollicular inflammation with plasma cells | Positive for telogen hairs |
| Temporal triangular alopecia | Lifelong, usually detected in infancy or childhood | Triangular or oval area with absent terminal hair in temporal region that is a few centimeters in diameter; vellus hairs visible on close inspection | N/A | Predominance of vellus hairs | Normal |
| Pressure-induced (postoperative) alopecia | Most commonly seen in surgical patients | Hair loss localized to area of prolonged pressure, such as the posterior scalp after prolonged general anesthesia | N/A | Nearly all hairs in catagen/telogen phase, trichomalacia¶, melanin in the collapsed outer root sheath, thrombosis, necrosis | Normal or positive |
| Patterned hair loss | |||||
| Male pattern hair loss (androgenetic alopecia in men) | Most common in adult men, prevalence increases with age | Slow, progressive terminal hair loss on the frontal, temporal, and/or vertex scalp | N/A | Marked variation in follicular size, increased proportion of vellus follicles, slight increase in telogen follicles, fibrous streamers beneath miniaturized hairs | Generally normal; may be positive in areas of active hair loss |
| Female pattern hair loss* | Most common in adult women, prevalence increases with age | Slow, progressive terminal hair loss and thinning on the crown of the scalp; frontal hairline is often relatively spared | If related to hyperandrogenism, signs of hirsutism or virilization may be present | Same as in male pattern hair loss | Generally normal; may be positive in areas of active hair loss |
| Trichotillomania | May occur in children and adults | Broken hairs often distributed in a bizarre pattern | May be associated with ingestion of hair and risk for trichobezoar | Follicular distortion, pigment casts, trichomalacia¶, melanin pigment in collapsed root sheaths, fractured hairs, follicular hemorrhage | Normal |
| Diffuse hair loss* | |||||
| Telogen effluvium | Women more likely to present for evaluation than men | Acute or chronic diffuse hair thinning | Findings associated with underlying cause may be present | Increase in the proportion of telogen follicles (20 to 50% of follicles are in telogen) | Positive in active phase; telogen hairs |
| Anagen effluvium | Seen in association with chemotherapy, radiation, toxins | Acute loss of hair | Findings associated with underlying cause may be present; hair loss in other sites | Increased proportion of telogen follicles, dystrophic anagen hairs; rare cases of permanent hair loss may demonstrate linear basaloid structures | Positive in active phase, dystrophic anagen hairs or broom-shaped anagen hairs with a pigmented bulb |
| Loose anagen syndrome | Affects children; most common in girls; often those with blond hair | Hair is easily dislodged from follicles without pain; hair density appears normal or reduced | May be solitary or associated with developmental defects | Dystrophic anagen hairs | Very positive; majority of hairs are anagen hairs with a ruffled cuticle and absent inner root sheath |
| Atrichia with papular lesions | Autosomal dominant disorder, presents in infancy | Hair normal at birth, hair loss in infancy due to abnormality in first hair cycle (defect in catagen phase); papular follicular cysts develop later | Hair loss and follicular cysts in other sites | Absence of mature hair follicles, cysts present | Normal; may be positive in initial stages |
| Hypotrichosis simplex | Group of hypotrichosis disorders; usually autosomal dominant | Usually progressive loss of scalp hair during childhood | May or may not have involvement of other hair-bearing sites | Reduced number of follicles, follicular miniaturization | Normal |
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