What causes hair loss?

Causes of Hair Loss

Hair loss is primarily caused by a combination of genetic predisposition, hormonal factors (particularly androgens), autoimmune conditions, nutritional deficiencies, and environmental stressors that affect the normal hair growth cycle. 1, 2, 3

Main Types and Causes of Hair Loss

Androgenetic Alopecia

• Most common form affecting up to 50% of white males by age 50 and 40% of women 2, 4
• Caused by:
  • Genetic predisposition (including androgen receptor gene) 2
  • Dihydrotestosterone (DHT) activity on susceptible hair follicles 3
  • Miniaturization of hair follicles due to shortened growth (anagen) cycles and prolonged rest (telogen) cycles 2
  • Decreased scalp microcirculation 5

Alopecia Areata

• Immune-mediated attack on hair follicles 6
• Contributing factors include:
  • Genetic susceptibility
  • Environmental triggers
  • Micronutrient deficiencies (particularly vitamin D, zinc, and folate) 6

Telogen Effluvium

• Characterized by diffuse shedding of hair
• Common triggers include: 1
  • Childbirth
  • Major surgery or severe illness
  • Sudden weight loss
  • Emotional stress
  • Iron deficiency
  • Thyroid disorders
  • Nutritional deficiencies
  • Certain medications (retinoids, antifungals, hormonal therapies)

Hormonal Factors in Hair Loss

• Androgens (particularly DHT) cause miniaturization of hair follicles in genetically predisposed individuals 3
• Estrogen deficiency (e.g., during menopause) can contribute to hair loss 3
• Thyroid dysfunction (both hypo- and hyperthyroidism) can cause various forms of hair loss 1, 3
• Stress hormones (cortisol, CRH, ACTH) play a role in stress-induced alopecia 3

Nutritional and Micronutrient Factors

• Iron deficiency is the most common nutritional deficiency associated with chronic diffuse telogen hair loss 1
• Vitamin D deficiency is linked to lower serum 25(OH)D levels in alopecia patients 1
• Zinc and folate deficiencies are more common in patients with alopecia areata 6
• Protein malnutrition can contribute to hair loss 1

Other Contributing Factors

• Comorbid medical conditions (endocrine disorders, metabolic syndrome) 4
• Medications and treatments (chemotherapy, certain drugs)
• Physical trauma to hair (traction, trichotillomania)
• Fungal infections (tinea capitis) 7

Clinical Pearls and Pitfalls

• Hair loss patterns help differentiate between types:

  • Androgenetic alopecia: temporal-frontal loss in men, central thinning in women 7
  • Alopecia areata: patchy loss
  • Telogen effluvium: diffuse thinning with "handfuls" of hair loss 7

• Diagnostic pitfalls to avoid:

  • Failing to identify underlying nutritional deficiencies
  • Overlooking hormonal disorders that may be causing or contributing to hair loss
  • Not recognizing that hair loss may be an early signal of systemic disease 4

• Treatment considerations:

  • FDA-approved treatments include topical minoxidil for men and women, and finasteride for men 7
  • Addressing underlying nutritional deficiencies and hormonal imbalances is essential 1