CAUSES AND RISK FACTORS

• Development is related to age and presence of androgenic hormones/receptors
• Alopecia areata: Although exact etiology is unknown, there is a genetic predisposition, and consensus favors an autoimmune response
• Telogen effluvium: Normal hair cycle is interrupted so that anagen (growing) hairs are abruptly converted into telogen (resting) hairs, which are subsequently shed after 2 to 4 months
• Hypothyroidism and hyperthyroidism
• Postpartum, post-illness
• Surgery with general anesthesia
• Nutritional deficiency, particularly with iron or zinc
• Psychological stress
• Most telogen effluvium from medications is caused by retinoids, β-blockers, calcium channel blockers, antidepressants, and nonsteroidal anti-inflammatory drugs (including ibuprofen)
• Tinea capitis: Ringworm of the scalp in which dermatophyte fungus invades the hair shaft. The most likely dermatophytes include
• Microsporum (from cats and dogs)

RISK FACTORS

1. Family history of baldness
2. Advanced age
3. Physical stress
4. Psychological stress
5. Pregnancy
6. Regular use of aggressive hair-styling techniques
7. Poor nutrition
8. Rapid weight loss
9. Restrictive diets (eg, low carbohydrate, low fat)

EPIDEMIOLOGY

Incidence and prevalence:

• About 25% of men aged 25 years have some degree of clinically apparent androgenic alopecia
• About 42% of men develop androgenic alopecia
• About 2% to 3% of the general population develops alopecia areata