Figure 1

Figure 2

Basics of Hair

3 Phases of Hair Development

1. Anagen (growing): 3-7 yr for scalp; 80%-90% of hairs; 50-100 switch to catagen/d (falling out)
2. Catagen (resting): 3-4 wk; 1% of hairs
3. Telogen (shedding): 3 mo; hairs have short club root; 50-100 hairs shed/day; 10%-15% of hairs in this phase

N.B.: Normal scalp contains 100,000 hairs. Blonds have 120,000 and those with red hair have 80,000 hairs. There are fewer hairs per square cm in Africans & Asians.

Drug Causes of Hair Loss

Diffuse Hair Loss

1. Alopecia areata (diffuse, although most commonly localized)
2. Drug-induced: cytotoxics, anticoagulants, retinoids
3. Endocrine disorders: hypothyroid, hypopituitarism
4. Hair-shaft defects: pili torti, monilethrix
5. Male-pattern baldness/androgenetic alopecia
6. Nutritional: iron deficiency
7. Syphilis
8. Systemic lupus erythematosus
9. Telogen effluvium

Localized Hair Loss

1. Alopecia areata
2. Discoid lupus erythematosus
3. Fungal infections (e.g., kerion)
4. Lichen planopilaris
5. Nevoid abnormalities
6. Traction (e.g., corn-rows, ponytails)
7. Trichotillomania

Nonscarring Alopecia: Intact Hair Follicles

1. Telogen effluvium (TE)
2. Alopecia areata (AA)
3. Anagen effluvium (following chemotherapy)
4. Androgenetic alopecia (AGA): male or female pattern baldness
5. Trichotillomania
6. Infections: fungal (i.e., tinea capitis, kerion)
7. Hair shaft abnormalities

Scarring alopecia: Loss of Hair Follicles^*

1. Discoid lupus erythematosus (DLE)
2. Lichen planopilaris (LPP)
3. Infections: fungal, bacterial, TB, leprosy

N.B.: If scalp biopsy performed (e.g., scarring alopecia), ideally a 4-mm punch biopsy is taken of a symptomatic or early active disease for transverse sectioning and H&E if lupus suspected, take additional 4-mm punch biopsy—bisect this piece vertically, and submit half for vertical sectioning, and half for DIF.

^* In general, scarring alopecias should be referred to a dermatologist.

See Topic(s):

• Alopecia Areata
• Androgenetic Alopecia (Male and Female Pattern Baldness)
• Telogen Effluvium
• Trichotillomania