Types of Hair Loss

Hair loss (alopecia) has many causes — correct diagnosis determines appropriate treatment. The main types:

  • Androgenetic alopecia (AGA): Most common type; affects 50% of men by 50 (male pattern baldness) and 25% of women (female pattern hair loss); driven by DHT sensitivity in genetically predisposed follicles; progressive miniaturization of hair shafts
  • Telogen effluvium (TE): Diffuse shedding triggered by physical or emotional stress 2–3 months after the trigger event (surgery, illness, crash dieting, childbirth, severe stress); typically self-resolving in 6 months once trigger addressed; chronic TE may indicate ongoing nutritional deficiency
  • Alopecia areata (AA): Autoimmune attack on hair follicles; circular patches of complete hair loss; affects 2% of the population; associated with thyroid disease and other autoimmune conditions; JAK inhibitors (baricitinib, ritlecitinib) now FDA-approved after decades without effective treatments
  • Traction alopecia: Mechanical hair loss from tight hairstyles (braids, extensions, tight ponytails); reversible if caught early; becomes permanent with prolonged tension
  • Scarring alopecias: Lichen planopilaris, frontal fibrosing alopecia — inflammatory conditions permanently destroy follicles; early treatment is critical

Androgenetic Alopecia: Mechanisms

AGA is the most understood and most treatable form of hair loss:

  • DHT pathway: Testosterone is converted to dihydrotestosterone (DHT) by 5-alpha-reductase in scalp follicles; DHT binds androgen receptors in genetically susceptible follicles, progressively shortening the anagen (growth) phase and miniaturizing the hair shaft over multiple cycles
  • Genetics: Polygenic inheritance; the androgen receptor gene (AR) on the X chromosome is the most important locus (explaining why male pattern baldness is often transmitted through the maternal line)
  • Female pattern hair loss (FPHL): Different distribution — diffuse thinning at the crown with preserved frontal hairline; androgen levels are often normal; local scalp sensitivity to androgens is the key factor; PCOS is a common underlying cause
  • Scalp microenvironment: DHT also promotes prostaglandin D2 (PGD2) production, which inhibits hair growth; conversely, prostaglandin E2 (PGE2) and F2α stimulate growth — this is the mechanism behind bimatoprost (prostaglandin analog) for eyebrow growth

Nutritional Causes of Hair Loss

Nutritional deficiencies are among the most common and most treatable causes of diffuse hair loss — yet are frequently missed:

  • Iron deficiency: Most common nutritional cause of hair loss in women; ferritin below 30 ng/mL is associated with telogen effluvium even without anemia; most trichologists target ferritin above 70 ng/mL for hair health; iron is essential for ribonucleotide reductase activity in rapidly dividing hair matrix cells
  • Vitamin D deficiency: VDRs are expressed in hair follicles and play a role in follicle cycling; multiple studies associate low vitamin D with alopecia areata and telogen effluvium; correction often improves shedding
  • Zinc deficiency: Hair loss is a classic deficiency symptom; zinc is required for protein synthesis in the hair matrix; seen in restrictive dieters, vegans, and those with GI absorption issues
  • Biotin: Only evidence-based in true biotin deficiency (rare); the widespread marketing of biotin for hair loss lacks clinical evidence in non-deficient people; raw egg white consumption causes biotin deficiency (avidin binding)
  • Protein deficiency: Hair is 95% keratin protein; severe caloric restriction and crash dieting cause telogen effluvium; adequate dietary protein (1.2–1.6g/kg) is foundational
  • Thyroid dysfunction: Both hypo and hyperthyroidism cause diffuse hair loss; TSH testing is mandatory in any hair loss workup

Medical Treatments: Evidence Summary

  • Minoxidil (topical 2–5%): First FDA-approved hair loss treatment; mechanism incompletely understood — extends anagen phase and increases follicle size; 5% more effective than 2% in men; women respond well to 2–5%; effects maintained only with continuous use; foam formulation better tolerated; oral low-dose minoxidil (0.25–1mg/day) growing evidence for both sexes with excellent efficacy
  • Finasteride (1mg/day oral): 5-alpha-reductase inhibitor; reduces scalp DHT by 60–70%; stops progression and regrows hair in 60–66% at 2 years; requires continuous use; sexual side effects in 1–2% (post-finasteride syndrome controversial but monitored); dutasteride (inhibits both type 1 and 2) more potent with stronger evidence
  • JAK inhibitors for alopecia areata: Baricitinib (Olumiant) and ritlecitinib (Litfulo) are FDA-approved for severe AA (2022–2023) — the first effective systemic treatments for this condition; produce complete or near-complete regrowth in 30–40% at 36 weeks
  • Platelet-rich plasma (PRP): Injections of concentrated growth factors from patient blood; growing evidence for AGA; multiple RCTs show significant hair density improvement; typically 3 sessions monthly then maintenance
  • Low-level laser therapy (LLLT): FDA-cleared devices (helmets, combs); improves hair density via mitochondrial stimulation; moderate evidence; useful adjunct especially for women
  • Hair transplantation: Follicular unit extraction (FUE) relocates DHT-resistant occipital hair to thinning areas; permanent results; requires stable donor area; appropriate after medical treatment optimization

Supplement Evidence for Hair Loss

  • Iron + ferritin optimization: The most evidence-supported supplement intervention for diffuse hair loss in women; target ferritin above 70 ng/mL; use ferrous bisglycinate for tolerability; retest at 3 months
  • Vitamin D: Correct deficiency to 40–60 ng/mL; evidence for alopecia areata and telogen effluvium; 2,000–4,000 IU/day typically required
  • Zinc: 25–40mg/day for documented deficiency; RCTs show modest benefit in alopecia areata; avoid excess (above 40mg/day competes with copper)
  • Saw palmetto (Serenoa repens): Mild 5-alpha-reductase inhibitor; 320mg/day standardized extract; multiple trials show modest hair density improvement in AGA; fewer sexual side effects than finasteride; evidence quality moderate
  • Pumpkin seed oil: 400mg/day shown in one RCT to increase hair count by 40% vs placebo in men with AGA; likely 5-alpha-reductase inhibitory mechanism
  • Collagen peptides: Provide glycine and proline for keratin synthesis; early evidence for hair growth; 2.5–5g/day hydrolyzed collagen; more data needed

Lifestyle & Scalp Health

  • Scalp health: Seborrheic dermatitis and scalp inflammation accelerate AGA progression; ketoconazole 2% shampoo (2x/week) has evidence for both dandruff control and mild hair growth promotion via anti-androgen and anti-inflammatory effects
  • Stress management: Chronic psychological stress elevates cortisol and prolongs telogen phase; acute severe stress causes telogen effluvium 2–3 months after the event; addressing ongoing stress reduces chronic shedding
  • Hair handling: Avoid excessive heat styling, chemical processing, and tight hairstyles; wet hair is most fragile — use wide-toothed comb, not brush; gentle detangling from ends upward
  • Sleep: Growth hormone (released during deep sleep) stimulates hair follicle activity; chronic sleep deprivation is associated with increased hair shedding
  • Exercise: Improves scalp microcirculation; reduces chronic stress cortisol; no direct hair growth evidence but general health benefits support follicle function

Frequently Asked Questions

Iron deficiency is the most common nutritional cause of hair loss in women — even without anemia; ferritin below 30 ng/mL is associated with telogen effluvium. Other important deficiencies include vitamin D (VDRs are expressed in hair follicles), zinc (essential for hair matrix protein synthesis), protein (hair is 95% keratin), and thyroid hormone (both hypo and hyperthyroidism cause diffuse shedding). A comprehensive blood panel including ferritin, TSH, vitamin D, and zinc is the recommended first step for any unexplained hair loss.

Yes — finasteride 1mg/day is one of the two most evidence-based treatments for male androgenetic alopecia. It reduces scalp DHT by 60–70%, stops progression in most men, and achieves visible regrowth in 60–66% at 2 years. It requires continuous use — effects reverse within 12 months of stopping. Sexual side effects occur in ~1–2% and are reversible in most cases upon discontinuation. Women of childbearing potential cannot use finasteride due to teratogenic risk.

Yes — both topical minoxidil (2–5%) and oral low-dose minoxidil (0.25–1mg/day) are effective for female pattern hair loss and telogen effluvium. Women respond well and tolerate the treatment with good safety profiles. The 5% foam formulation is commonly used. Oral minoxidil at low doses is gaining strong evidence with fewer cosmetic side effects than higher doses. Effects require 4–6 months to assess and maintenance is required.

Yes — acute severe stress (surgery, illness, major life event, crash dieting) causes telogen effluvium: diffuse shedding that begins 2–3 months after the stressor. This is because stress shifts follicles from the growth phase (anagen) to the resting phase (telogen) en masse. The good news is telogen effluvium is typically self-resolving within 6 months once the stress trigger is removed and nutritional status is adequate.

A comprehensive hair loss panel should include: serum ferritin (target above 70 ng/mL for hair health, not just above lab range), CBC (anemia), TSH (thyroid), 25-OH Vitamin D, zinc, total testosterone and DHEAS (in women with suspected hormonal cause), prolactin, and a comprehensive metabolic panel. This covers the most common and treatable causes. Anti-nuclear antibodies (ANA) may be added if autoimmune alopecia is suspected.

Research Summary

Hair loss has multiple distinct causes requiring targeted treatment. Iron optimization, vitamin D, and thyroid correction address the most common nutritional causes; minoxidil and finasteride are the gold-standard medical treatments for AGA.

  • Evidence strength: Strong (4/5)
  • Most common cause: Androgenetic alopecia (DHT-mediated follicle miniaturization)
  • First-line AGA: Minoxidil (topical/oral) + finasteride (men) or spironolactone (women)
  • Most missed cause: Iron deficiency — target ferritin above 70 ng/mL, not just lab normal
  • AA breakthrough: JAK inhibitors (baricitinib, ritlecitinib) FDA-approved 2022–2023
  • Key testing: Ferritin, TSH, vitamin D, zinc before supplementation
⚠️ Medical Disclaimer: This content is for informational purposes only and is not intended as medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making health decisions.

References

All studies cited are peer-reviewed. DOI and PubMed links open in a new tab.

  1. 1. Blumeyer A, Tosti A, Messenger A, et al. (2011). Evidence-based (S3) guideline for the treatment of androgenetic alopecia in women and in men. Journal of the German Society of Dermatology, 9 Suppl 6, S1–57. doi:10.1111/j.1610-0379.2011.07802.x PMID:21980982
  2. 2. King B, Ohyama M, Kwon O, et al. (2022). Two Phase 3 Trials of Baricitinib for Alopecia Areata. New England Journal of Medicine, 386(18), 1687–1699. doi:10.1056/NEJMoa2110343 PMID:35334197
  3. 3. Rasheed H, Mahgoub D, Hegazy R, et al. (2013). Serum ferritin and vitamin D in female hair loss: do they play a role?. Skin Pharmacology and Physiology, 26(2), 101–107. doi:10.1159/000346698 PMID:23407001
  4. 4. Kil MS, Kim CW, Kim SS (2013). Analysis of serum zinc and copper concentrations in hair loss. Annals of Dermatology, 25(4), 405–409. doi:10.5021/ad.2013.25.4.405 PMID:24371385
  5. 5. Cho YH, Lee SY, Jeong DW, et al. (2014). Effect of pumpkin seed oil on hair growth in men with androgenetic alopecia: a randomized, double-blind, placebo-controlled trial. Evidence-Based Complementary and Alternative Medicine, 2014, 549721. doi:10.1155/2014/549721 PMID:25210906
  6. 6. Mysore V, Arghya A (2022). Hair Oils: Indigenous Knowledge Revisited. International Journal of Trichology, 14(3), 84–90. doi:10.4103/ijt.ijt_189_20 PMID:35755964
  7. 7. Truchetet ME, Chiche L, Barnetche T, Faure V (2023). Ritlecitinib for the treatment of alopecia areata: systematic review and meta-analysis. Journal of the American Academy of Dermatology, 89(4), 832–834. doi:10.1016/j.jaad.2023.05.074 PMID:37276969
  8. 8. Price VH (1999). Treatment of hair loss. New England Journal of Medicine, 341(13), 964–973. doi:10.1056/NEJM199909233411307 PMID:10498493