Hair loss (alopecia) is a common presenting concern in dermatologic practice and affects individuals of all ages and genders. Normal physiologic shedding of approximately 50–100 hairs per day reflects normal hair cycling; however, persistent thinning, excessive shedding, or focal hair loss warrants clinical evaluation.¹ Hair loss may arise from intrinsic follicular disorders, systemic disease, hormonal imbalance, nutritional deficiency, or external mechanical factors.¹
Hair Biology and the Hair Cycle
Hair follicles undergo a continuous, cyclical process consisting of three distinct phases:¹
- Anagen (growth phase): Active hair fiber production
- Catagen (transition phase): Brief follicular involution
- Telogen (resting phase): Hair shedding followed by re-entry into anagen
At any given time, approximately 85–90% of scalp hairs are in anagen.¹ Disruption of normal cycling, follicular miniaturization, or irreversible follicular destruction results in clinically apparent hair loss.¹
Androgenetic Alopecia (Pattern Hair Loss)
Definition
Androgenetic alopecia is the most common cause of hair loss in adults.²
Pathophysiology
In genetically predisposed individuals, increased follicular sensitivity to androgens, particularly dihydrotestosterone (DHT), leads to progressive miniaturization of terminal hair follicles and shortening of the anagen phase.²
Clinical Features
- Men: Bitemporal recession and vertex thinning²
- Women: Diffuse thinning over the central scalp with relative preservation of the frontal hairline³
Epidemiology
The prevalence of androgenetic alopecia increases with age, affecting the majority of men and a substantial proportion of women over their lifetime.²,³
Genetics is efficient, if not always kind. This is one family trait most people would happily decline; unfortunately, genetics rarely asks for consent.
Telogen Effluvium
Definition
Telogen effluvium is a reactive, non-scarring alopecia characterized by diffuse hair shedding due to premature transition of hair follicles into the telogen phase.⁴
Common Triggers
- Acute or chronic systemic illness, surgery, or febrile episodes⁴
- Significant physiological or psychological stress⁴
- Rapid weight loss or nutritional disruption⁴
- Pregnancy and the postpartum period⁵
Clinical Pattern
Hair shedding typically begins 2–3 months after the inciting event and may persist for several months.⁴ Regrowth generally occurs within 6–12 months once the trigger resolves.⁴,⁵
Autoimmune Disorders: Alopecia Areata
Definition
Alopecia areata is a non-scarring autoimmune disorder affecting anagen hair follicles.⁶
Pathogenesis
Loss of follicular immune privilege allows cytotoxic T-cell-mediated inflammation, leading to abrupt cessation of hair growth.⁶
Clinical Features
- Well-demarcated, round or oval patches of complete hair loss⁶
- Possible nail pitting⁶
- Severe cases may progress to alopecia totalis or alopecia universalis⁶
Despite its sudden onset, follicles remain viable, and spontaneous regrowth may occur.⁶
Hormonal and Endocrine Factors
Hormonal regulation significantly influences hair follicle cycling:
- Androgens contribute to follicular miniaturization in androgenetic alopecia²
- Thyroid dysfunction (hyperthyroidism or hypothyroidism) is associated with diffuse hair shedding⁸
- Pregnancy, postpartum hormonal changes, and menopause alter hair cycle dynamics and shedding patterns⁵
Hair often reflects hormonal imbalance before other symptoms become evident.
Nutritional Deficiencies
Adequate nutrition is essential for normal hair growth and follicular function.¹
Deficiencies associated with hair loss include:
- Iron deficiency, a common and potentially reversible cause, particularly in women⁷
- Protein deficiency⁷
- Zinc, vitamin D, and selected B-vitamin deficiencies⁷
Laboratory testing should guide supplementation, as routine high-dose vitamin use without documented deficiency is not recommended.⁷
More supplements do not equal more hair!
Medications and Systemic Illness
Hair loss may result from pharmacologic therapy or systemic disease:
- Chemotherapy agents commonly cause anagen effluvium⁸
- Medications such as anticoagulants, beta-blockers, retinoids, anticonvulsants, and some antidepressants may induce telogen effluvium⁵,⁸
- Chronic systemic diseases, including autoimmune, metabolic, and endocrine disorders, can indirectly disrupt the hair cycle⁸
Temporal correlation with new medications should prompt review rather than assumption.
Mechanical and External Factors
- Traction alopecia, caused by prolonged mechanical tension from hairstyles, may result in permanent follicular damage if unaddressed⁹
- Chemical processing and thermal styling primarily damage the hair shaft but may contribute to hair loss when excessive or combined with traction⁸
If a hairstyle causes pain, it is providing clinically useful feedback.
Scarring (Cicatricial) Alopecias
Scarring alopecias are inflammatory disorders resulting in irreversible destruction of hair follicles. Common examples include lichen planopilaris, frontal fibrosing alopecia, and central centrifugal cicatricial alopecia.¹⁰ Early diagnosis and intervention are essential to prevent permanent hair loss.¹⁰
Clinical Approach
Evaluation of hair loss should include:
- Detailed history (onset, pattern, and progression)¹⁰
- Medication and systemic illness review⁸
- Nutritional and endocrine assessment⁷,⁸
- Scalp examination with trichoscopy¹⁰
Scalp biopsy may be required in atypical cases or when scarring alopecia is suspected.¹⁰
Summary
Hair loss is a multifactorial clinical presentation with diverse etiologies:
- Androgenetic alopecia — genetic and hormonal²,³
- Telogen effluvium — reactive shedding⁴,⁵
- Alopecia areata — autoimmune⁶
- Hormonal and endocrine disorders⁸
- Nutritional deficiencies⁷
- Medications and systemic illness⁸
- Mechanical and external factors⁹
- Scarring alopecias — irreversible follicular destruction¹⁰
Accurate diagnosis enables targeted, individualized management and improved patient outcomes.
Common Myths About Hair Loss
Myth 1: Hair loss means poor health
Fact: Most hair loss occurs in otherwise healthy individuals and is commonly genetic or age-related.²
Myth 2: Washing hair causes hair loss
Fact: Hair washing does not cause hair loss; shed hairs were already in the telogen phase.¹
Myth 3: Hats and helmets cause baldness
Fact: There is no evidence that headwear causes hair loss. Follicles are nourished by blood supply, not air.²
Myth 4: Hair loss only comes from the mother's side
Fact: Androgenetic alopecia is polygenic, involving both maternal and paternal inheritance.²,³ Blaming only one side of the family may be emotionally satisfying, but it is genetically inaccurate.
Myth 5: Stress causes immediate hair loss
Fact: Stress-related shedding typically occurs 2–3 months after the inciting event.⁴,⁵ Hair has an excellent memory and a very slow reaction time.
Myth 6: Hair loss is always permanent
Fact: Many forms of hair loss are non-scarring and reversible.⁴–⁶
Myth 7: More vitamins equal better hair growth
Fact: Supplements only benefit hair growth when a deficiency exists; excess intake may worsen hair loss.⁷
Myth 8: One treatment works for all hair loss
Fact: Treatment effectiveness depends on accurate diagnosis and underlying etiology.²,⁶
Myth 9: Tight hairstyles only cause temporary loss
Fact: Chronic traction can lead to permanent follicular damage.⁹
Myth 10: Hair loss is purely cosmetic
Fact: Hair loss can significantly impact psychological well-being and quality of life.²,⁶
