Why Hair Loss Happens and How to Stop It: A Complete Evidence Based Medical Guide (2025).


Dr JK Avhad MBBS MD [Last updated 28.12.2025]

An estimated 50–60% of men and up to 40% of women experience noticeable hair loss at some point in their lives, globally. Although hair fall is often assumed to be a cosmetic problem, it carries significant psychological, social, and emotional impact, affecting self-esteem, confidence, interpersonal relationships, and quality of life. Understanding the underlying causes, identifying early warning signs, seeking timely medical advice, and adopting evidence based treatment can significantly improve outcomes.

This detailed guide provides a scientific, structured, and comprehensive review of hair loss, including its physiology, major causes, diagnostic approach, management strategies, and preventive measures.

Introduction to Hair Physiology

Hair is a complex biological structure composed of keratin. Each hair follicle undergoes a cyclical growth process:

Anagen [ Growth Phase ]

·       Lasts 2–7 years.

·       Determines hair length

·       85–90% of scalp hairs are in anagen.

Catagen [ Transition Phase ]

·       Lasts 2–3 weeks.

·       Hair follicle shrinks; growth stops.

Telogen  [ Resting Phase ]

·       Lasts 2–4 months.

·       10–15% of hairs are in this phase.

Exogen  [ Shedding Phase ]

·       Hair is released and shed.

·       Normal shedding: 50–150 hairs/day.

Disturbances in these phases, especially increased telogen shedding or miniaturization of follicles, lead to hair loss.

Classification of Hair Loss

Hair loss is broadly classified into:

    Non-scarring (Reversible) Alopecia

The most common and treatable category.

Androgenetic Alopecia

It is a pattern of hair loss. Most common cause in both men and women.

  • Men: receding hairline, frontal thinning, vertex balding.
  • Women: diffuse thinning over crown with preserved hairline.

 Mechanism: Genetic predisposition  causes increased sensitivity to DHT (dihydrotestosterone), and miniaturization of hair follicles, results in shortened anagen phase.

Telogen Effluvium

Sudden, diffuse hair loss.

Triggers:

  • Physical or emotional stress
  • Fever, illness, infections
  • Childbirth
  • Crash dieting, protein deficiency
  • Surgeries
  • Thyroid disorders
  • Medications like retinoids, anti-hypertensives, oral contraceptive pills [ OCPs ], antidepressants.
  • Iron deficiency

Usually reversible.

Alopecia Areata

Autoimmune condition causing patchy hair loss.

Variants:

  • Patchy AA
  • Ophiasis pattern
  • Alopecia totalis –Hair loss over entire scalp
  • Alopecia universalis—Hair loss over entire body

Often associated with autoimmune diseases like thyroiditis, vitiligo.

Traction Alopecia

Due to chronic pulling from hairstyles:

  • Tight buns
  • Ponytails
  • Braids
  • Hair extensions

Early stages reversible but prolonged traction causes scarring.

Anagen Effluvium

Rapid hair loss due to:

  • Chemotherapy
  • Radiotherapy
  • Poisoning due to severe toxins like arsenic, thallium

Hair usually regrows after treatment ends.

Nutritional Alopecia

Due to deficiency of:

  • Iron
  • Vitamin D
  • Zinc
  • Biotin
  • Protein
  • Essential fatty acids

    Scarring (Cicatricial) Alopecia

Permanent destruction of hair follicles.

Causes include:

  • Lichen planopilaris
  • Discoid lupus erythematosus
  • Folliculitis decalvans
  • Central centrifugal cicatricial alopecia (common in African descent)

Requires early diagnosis to prevent permanent loss.

Major Causes of Hair Loss

Hair loss is multifactorial. Key culprits include:

Genetic Factors

      Hereditary pattern of hair loss is the dominant cause in both sexes. Polymorphisms of androgen receptor genes influence follicular sensitivity to DHT.

Hormonal Causes

DHT & Androgen Sensitivity

  •       DHT shrinks hair follicles in genetically susceptible individuals.

Thyroid Disorders

  •       Both hyperthyroidism and hypothyroidism cause hair thinning.

PCOS (in women)

  •       Insulin resistance causes excess androgens production and resultant hair thinning & hirsutism.

Postpartum Hormonal Shifts

  •       Estrogen decline causes telogen effluvium.

Menopause

  •       Low estrogen affects the growth cycle.

Stress

  •       Physical and emotional stress pushes hair into telogen phase, causing shedding.

Nutritional Deficiencies

Deficiencies strongly linked to hair loss:

  • Iron
  • Vitamin D
  • Vitamin B12
  • Zinc
  • Selenium
  • Protein/calorie deficiency
  • Omega-3 fatty acids

Autoimmune Disorders

Alopecia areata and similar diseases attack hair follicles.

Infections

  • Fungal infections (tinea capitis)
  • Bacterial folliculitis
  • Viral infections

 Medications

Common culprits:

  • Chemotherapy
  • Antidepressants (like SSRIs)
  • Blood thinners
  • Antihypertensives
  • Retinoids
  • Anticonvulsants
  • Oral contraceptive control pills

 

Hair Styling & Chemical Damage

  • Frequent coloring
  • Bleaching
  • Rebonding
  • Keratin treatments
  • Heat styling
  • Traction hairstyles

Diagnosis of Hair Loss

A good diagnosis is the foundation of effective treatment.

Detailed Clinical History

Includes:

  • Onset, duration, pattern
  • Recent stress or illness
  • Menstrual & hormonal history
  • Diet history
  • Hair care practices
  • Family history

 Physical Examination

  • Distribution of hair loss
  • Scalp condition
  • Follicular openings (visible/open = non-scarring)
  • Hair density

Diagnostic Tests

Pull Test

  •       Positive if >6 hairs come out when gently pulled.

Trichoscopy

  •       Helps to differentiate types of alopecia.

Laboratory Tests

  • Complete blood count
  • Serum ferritin
  • Serum iron
  • Serum TSH / T3 / T4
  • Vitamin D
  • B12
  • Zinc
  • Biochemical studies—blood level of hormones like testosterone, DHEAS

Scalp Biopsy

      Needed in scarring alopecia.

Management of Hair Loss

Treatment depends on the cause. Early intervention gives the best outcomes.

Androgenetic Alopecic

Topical Minoxidil

Most evidence based treatment.

  • Available in 2%, 5%, 10% solutions/foams.
  • Increases blood flow and prolongs anagen phase.
  • Results visible after 3–6 months.
  • Side effects: itching, dandruff, initial shedding.

Finasteride

Men only medication. Blocks DHT formation.

  • Dose: 1 mg/day.
  • Highly effective for male pattern baldness.

Dutasteride

      More potent DHT blocker; used selectively.

Anti-androgens (for women)

For PCOS related hair thinning.

  • Spironolactone
  • Cyproterone acetate
  • Oral contraceptives

PRP Therapy (Platelet-Rich Plasma)

Injecting activated platelets stimulates follicular growth.

  • 3–4 sessions
  • Visible improvement in density & thickness.

Microneedling

      Creates micro-injuries stimulating hair growth; often combined with minoxidil.

Hair Transplant

      Used for advanced AGA.

Techniques:

  • FUE (Follicular Unit Extraction)
  • FUT (Strip method)

Results are permanent if performed properly.

Telogen Effluvium Management

Key steps:

  • Identify and treat the trigger.
  • Correct deficiencies (of iron, vitamin D, B12, zinc).
  • Stress reduction.
  • High protein diet.
  • Gentle hair care.

Most recover in 3–6 months.

Alopecia Areata Treatment

First-line:

  • Topical corticosteroids
  • Intralesional steroid injection

Second-line:

  • Topical immunotherapy
  • PRP
  • Minoxidil

Severe cases:

  • JAK inhibitors (tofacitinib, baricitinib) — under specialist supervision.

Nutritional Treatment

Important supplements:

  • Iron
  • Vitamin D
  • Zinc
  • Biotin
  • Omega-3 fatty acids
  • Protein

Scalp Infections

  • Antifungal shampoos (ketoconazole)
  • Oral antifungals
  • Antibiotics for bacterial infections

Traction Alopecia

  • Immediate removal of traction hairstyles.
  • Minoxidil may help in early stages.
  • Long-standing cases may require transplantation.

Lifestyle Measures for Hair Health

Nutrition

A balanced diet rich in:

  • Lean protein
  • Eggs, fish
  • Nuts/seeds
  • Green leafy vegetables
  • Fruits
  • Pulses
  • Dairy

Avoid:

  • Crash diets
  • Severe calorie restrictions
  • Junk foods & processed sugars

Stress Management

Evidence shows strong link between chronic stress and hair loss.

Helpful methods:

  • Meditation
  • Yoga
  • Mindfulness
  • Deep breathing
  • Adequate sleep
  • Regular exercise

Hair Care Practices

  • Use mild shampoos.
  • Avoid daily heat styling.
  • Reduce chemical treatments.
  • Avoid tight hairstyles.
  • Limit hair coloring to 6–8 week intervals.

 

Prevention of Hair Loss

Maintain healthy scalp

  • Regular cleansing
  • Anti-dandruff care
  • Avoid harsh products

Adequate nutrition

  •       Especially iron, protein, vitamin D.

Protect follicles

  •       Minimal traction, minimal heat.

Early treatment

  •       For AGA, early intervention strongly improves outcomes.

Manage medical conditions

  •       Diabetes, thyroid disease, anemia, PCOS must be controlled

When to See a Dermatologist

Consult a specialist if:

  • Hair fall >150 hairs/day
  • Sudden or patchy loss
  • Bald patches
  • Severe dandruff or scalp infection
  • Pain, redness, scaling
  • Progressive thinning
  • Family history of baldness
  • Persistent shedding >6 months

Early diagnosis prevents irreversible loss.

Conclusion

Hair loss is a widespread condition influenced by genetics, hormones, nutrition, lifestyle factors, stress, medical illnesses, and hair care practices. While some types such as androgenetic alopecia are progressive, early treatment significantly improves outcomes. Others, like telogen effluvium or nutritional hair loss, are reversible with appropriate care. Understanding the underlying cause is the most important first step.

Treatments today, from minoxidil and nutritional correction to PRP and hair transplant, provide effective and scientifically backed solutions. Preventive measures such as balanced nutrition, stress control, and gentle hair practices play a crucial role in maintaining scalp and hair health.

This article is for informational purpose only and does not substitute for professional medical advise. For proper diagnosis and treatment seek the help of your healthcare provider.

References:

  1. Norwood OT. Male pattern baldness: classification and incidence. South Med J. 1975.
  2. Cash TF. The psychology of hair loss. Clin Dermatol. 2001.
  3. Stenn KS, Paus R. Controls of hair follicle cycling. Physiol Rev. 2001.
  4. Messenger AG. The control of hair growth. Clin Dermatol. 1988.
  5. Sinclair R. Male androgenetic alopecia. BMJ. 1998.
  6. Headington JT. Telogen effluvium. Arch Dermatol. 1993.
  7. Gilhar A et al. Alopecia areata. NEJM. 2012.
  8. Khumalo NP. Traction alopecia. J Am Acad Dermatol. 2007.
  9. Trueb RM. Chemotherapy-induced alopecia. Dermatology. 2009.
  10. Rushton DH. Nutritional factors in hair loss. Clin Exp Dermatol. 2002.
  11. Olsen EA. Cicatricial alopecia. Dermatol Clin. 1999.
  12. Hillmer AM et al. Genetic variants in AGA. Nat Genet. 2005.
  13. Kaufman KD. Finasteride mechanism. J Clin Endocrinol Metab. 1998.
  14. Arck PC et al. Stress and hair loss. Am J Pathol. 2001.
  15. Kantor J et al. Iron deficiency and hair loss. J Am Acad Dermatol. 2003.
  16. McElwee KJ. Autoimmunity in alopecia areata. Dermatol Clin. 2013.
  17. Jimenez JJ. Drug-induced alopecia. Dermatol Clin. 2007.
  18. Rakowska A. Trichoscopy in alopecia. J Dermatol Case Rep. 2008.
  19. Elston DM. Hair biopsy interpretation. Am J Dermatopathol. 2008.
  20. Olsen EA. Minoxidil trials. J Am Acad Dermatol. 1989.
  21. Roberts JL. Finasteride efficacy. J Am Acad Dermatol. 1999.
  22. Vexiau P. Anti-androgens in female alopecia. Clin Endocrinol. 1986.
  23. Gentile P et al. PRP in alopecia. Dermatol Surg. 2015.
  24. Unger WP. Hair transplantation. Dermatol Clin. 1996.
  25. Porter D. Intralesional steroids in AA. Arch Dermatol. 1960.
  26. Mackay-Wiggan J et al. JAK inhibitors in AA. JCI Insight. 2016.
  27. Almohanna HM et al. Nutrition and hair. Dermatol Pract Concept. 2019.
Scroll to Top