{"id":14879,"date":"2026-05-29T06:00:00","date_gmt":"2026-05-29T10:00:00","guid":{"rendered":"https:\/\/cov19longhaulfoundation.org\/?p=14879"},"modified":"2026-05-16T10:11:52","modified_gmt":"2026-05-16T14:11:52","slug":"covid-19-and-hair-follicle-biology-mechanisms-of-alopecia-telogen-effluvium-molecular-injury-and-clinical-management","status":"publish","type":"post","link":"https:\/\/cov19longhaulfoundation.org\/?p=14879","title":{"rendered":"COVID-19 and Hair Follicle Biology: Mechanisms of Alopecia, Telogen Effluvium, Molecular Injury, and Clinical Management"},"content":{"rendered":"\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Abstract<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2, is associated with a broad spectrum of post-infectious dermatologic sequelae, among which diffuse hair loss\u2014most commonly telogen effluvium (TE)\u2014is increasingly recognized. Hair follicle dysfunction appears to result from a convergence of systemic inflammation, cytokine-mediated follicular cycling disruption, hypoxic stress, and metabolic reprogramming of keratinocytes. Emerging molecular studies also suggest potential direct viral interaction with follicular epithelial structures. This review synthesizes current evidence regarding the pathophysiology, protein-level alterations, clinical presentation, and management strategies for COVID-19\u2013associated hair disorders.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">1. Introduction: Hair Follicles as a Dynamic Immunometabolic Organ<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The human hair follicle is not merely a keratin-producing appendage but a highly active <strong>immunologically privileged mini-organ<\/strong> with cyclical phases of growth (anagen), regression (catagen), and rest (telogen). Disruption of this cycle can result in diffuse shedding or structural alopecia.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">COVID-19 has been associated primarily with <strong>telogen effluvium<\/strong>, a condition characterized by premature transition of hair follicles into the telogen phase following systemic stressors.\u00b9<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Unlike scarring alopecias, TE is typically reversible; however, COVID-19 appears to produce a <strong>more synchronized and abrupt follicular shift<\/strong>, suggesting a distinct inflammatory or metabolic trigger compared with classic stress-induced TE.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">2. Hair Cycle Physiology and Vulnerability to Systemic Disease<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">2.1 Anagen phase (growth)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">During anagen, follicular keratinocytes undergo rapid proliferation requiring:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>high oxygen availability<\/li>\n\n\n\n<li>robust mitochondrial ATP production<\/li>\n\n\n\n<li>tightly regulated Wnt\/\u03b2-catenin signaling<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Any systemic disturbance affecting energy metabolism or inflammatory signaling can prematurely terminate this phase.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2.2 Catagen phase (regression)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Catagen is driven by:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>apoptosis of matrix keratinocytes<\/li>\n\n\n\n<li>reduced dermal papilla signaling<\/li>\n\n\n\n<li>increased TGF-\u03b2 activity<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">COVID-19\u2013associated cytokine storms may accelerate catagen entry.\u00b2<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2.3 Telogen phase (rest)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Telogen follicles remain quiescent until reactivation. A large proportion entering telogen simultaneously results in diffuse shedding 2\u20133 months later.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">3. Telogen Effluvium as the Dominant COVID-19 Hair Disorder<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Multiple systematic reviews confirm TE as the most common post-COVID alopecia phenotype.\u00b3<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Key clinical characteristics include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>diffuse non-scarring shedding<\/li>\n\n\n\n<li>onset 1\u20133 months post infection<\/li>\n\n\n\n<li>female predominance (~70\u201385%)<\/li>\n\n\n\n<li>high reversibility (>90%) within 6 months in most cohorts\u2074<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">This pattern is consistent with systemic physiological stress rather than localized follicular disease.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">4. Systemic Inflammatory Mechanisms<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">4.1 Cytokine storm\u2013mediated follicular arrest<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">COVID-19 is characterized by elevated:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>IL-6<\/li>\n\n\n\n<li>TNF-\u03b1<\/li>\n\n\n\n<li>IL-1\u03b2<\/li>\n\n\n\n<li>interferon signaling pathways<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">These cytokines directly influence follicular cycling by:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>suppressing Wnt signaling (anagen maintenance)<\/li>\n\n\n\n<li>promoting premature catagen entry<\/li>\n\n\n\n<li>altering dermal papilla signaling integrity<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">IL-6 in particular has been shown to inhibit epithelial proliferation in multiple keratinized tissues.\u2075<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">4.2 Autoimmune activation hypothesis<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Post-viral immune dysregulation may lead to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>transient loss of follicular immune privilege<\/li>\n\n\n\n<li>increased CD8+ T-cell infiltration<\/li>\n\n\n\n<li>autoimmune-like follicular stress responses<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">This may explain prolonged or relapsing shedding in long COVID patients.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">5. Vascular and Hypoxic Contributions<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">SARS-CoV-2\u2013induced endothelial dysfunction contributes to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>microvascular hypoperfusion of hair follicles<\/li>\n\n\n\n<li>reduced dermal papilla oxygenation<\/li>\n\n\n\n<li>impaired nutrient delivery<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Histopathologic evidence demonstrates widespread endothelial inflammation in COVID-19 systemic disease.\u2076<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Hypoxia further induces:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>HIF-1\u03b1 upregulation<\/li>\n\n\n\n<li>metabolic suppression of follicular stem cells<\/li>\n\n\n\n<li>mitochondrial dysfunction in rapidly dividing matrix keratinocytes<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">6. Direct Viral and Molecular Follicular Effects<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Recent ex vivo studies have demonstrated:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>ACE2 and TMPRSS2 expression in hair follicle structures<\/li>\n\n\n\n<li>potential viral spike protein presence in follicular epithelium\u2077<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">This raises the possibility of:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>direct follicular epithelial infection<\/li>\n\n\n\n<li>local immune activation within follicular units<\/li>\n\n\n\n<li>disruption of stem cell niches in the bulge region<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Although still under investigation, this mechanism may explain more severe or persistent cases.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">7. Protein-Level and Molecular Changes in Hair Follicles<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">COVID-19\u2013associated follicular stress induces measurable molecular changes:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">7.1 Keratin alterations<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>reduced K31\/K86 keratin expression<\/li>\n\n\n\n<li>altered hair shaft structural integrity<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">7.2 Growth signaling disruption<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>downregulation of \u03b2-catenin pathway<\/li>\n\n\n\n<li>increased TGF-\u03b2 and FGF suppression<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">7.3 Stress-response proteins<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>increased heat shock proteins (HSP70)<\/li>\n\n\n\n<li>oxidative stress markers (ROS accumulation)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">7.4 Proteoglycan and extracellular matrix changes<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Systemic inflammation alters dermal papilla extracellular matrix composition, affecting follicle anchoring and cycling stability.\u2078<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">8. Clinical Phenotypes of COVID-19\u2013Associated Hair Loss<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">8.1 Acute telogen effluvium<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>diffuse shedding<\/li>\n\n\n\n<li>onset ~2 months post infection<\/li>\n\n\n\n<li>self-limited in majority<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">8.2 Chronic telogen effluvium<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>prolonged shedding beyond 6 months<\/li>\n\n\n\n<li>often associated with persistent systemic inflammation or long COVID<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">8.3 Anagen effluvium (rare)<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>seen in severe systemic illness<\/li>\n\n\n\n<li>rapid hair loss during active disease phase<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">8.4 Mixed inflammatory alopecia<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>overlap with androgenetic alopecia unmasking<\/li>\n\n\n\n<li>inflammatory scalp involvement in subset of patients<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">9. Clinical Course and Prognosis<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A systematic review of COVID-associated TE demonstrated:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>median onset: ~2 months post infection<\/li>\n\n\n\n<li>median duration: ~5 months<\/li>\n\n\n\n<li>resolution rate: ~90\u201395% in most cohorts\u2079<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">However, a subset of patients reports persistent shedding beyond 12\u201324 months, particularly in long COVID populations.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">10. Diagnostic Evaluation<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Recommended evaluation includes:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>ferritin and iron studies<\/li>\n\n\n\n<li>thyroid function testing<\/li>\n\n\n\n<li>vitamin D levels<\/li>\n\n\n\n<li>inflammatory markers (CRP, ESR)<\/li>\n\n\n\n<li>dermatologic examination with trichoscopy<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Scalp biopsy is rarely required unless scarring alopecia is suspected.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Footnotes (Vancouver Style \u2014 Part I)<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Malkud S. Telogen effluvium: a review. <em>J Clin Diagn Res.<\/em> 2015.<\/li>\n\n\n\n<li>Paus R, Cotsarelis G. The biology of hair follicles. <em>N Engl J Med.<\/em> 1999.<\/li>\n\n\n\n<li>Mieczkowska K et al. Hair loss in COVID-19 patients. <em>J Am Acad Dermatol.<\/em> 2021.<\/li>\n\n\n\n<li>Starace M et al. Post-COVID telogen effluvium. <em>Dermatol Ther.<\/em> 2020.<\/li>\n\n\n\n<li>Del Valle DM et al. Cytokine profiles in COVID-19. <em>Nat Med.<\/em> 2020.<\/li>\n\n\n\n<li>Ackermann M et al. Vascular pathology in COVID-19. <em>N Engl J Med.<\/em> 2020.<\/li>\n\n\n\n<li>Klingenstein S et al. Spike protein in hair follicles. <em>Sci Rep.<\/em> 2025.<\/li>\n\n\n\n<li>Rossi A et al. Telogen effluvium mechanisms in SARS-CoV-2 infection. <em>Skin Appendage Disord.<\/em> 2021.<\/li>\n\n\n\n<li>Gupta AK et al. COVID-19 hair loss systematic review. <em>J Eur Acad Dermatol Venereol.<\/em> 2021.<\/li>\n\n\n\n<li>Hussain N et al. Acute telogen effluvium post COVID-19. <em>J Med Virol.<\/em> 2021.<\/li>\n\n\n\n<li>Rebora A. Telogen effluvium pathophysiology. <em>Dermatology.<\/em> 2010.<\/li>\n\n\n\n<li>Tr\u00fceb RM. Stress and hair loss. <em>Exp Dermatol.<\/em> 2009.<\/li>\n\n\n\n<li>Li Y et al. Hair follicle immune privilege. <em>J Invest Dermatol.<\/em> 2019.<\/li>\n\n\n\n<li>Stenn KS, Paus R. Controls of hair follicle cycling. <em>Physiol Rev.<\/em> 2001.<\/li>\n\n\n\n<li>WHO COVID-19 Clinical Characterization Consortium. <em>Lancet.<\/em> 2020.<\/li>\n\n\n\n<li>Daneshgaran G et al. Dermatologic COVID-19 manifestations. <em>Dermatol Ther.<\/em> 2020.<\/li>\n\n\n\n<li>Vabres P et al. Hair cycle inflammatory regulation. <em>Br J Dermatol.<\/em> 2018.<\/li>\n\n\n\n<li>Fabbrocini G et al. Hair disorders review. <em>Dermatol Clin.<\/em> 2019.<\/li>\n\n\n\n<li>Tobin DJ. Hair follicle immunology. <em>Exp Dermatol.<\/em> 2017.<\/li>\n\n\n\n<li>Semenza GL. Hypoxia signaling pathways. <em>Cell.<\/em> 2012.<\/li>\n\n\n\n<li>Wnt\/\u03b2-catenin signaling in hair growth regulation. <em>Nature.<\/em> 2015.<\/li>\n\n\n\n<li>Cotsarelis G. Stem cells in hair follicles. <em>Science.<\/em> 1990.<\/li>\n\n\n\n<li>Sperling LC. Telogen effluvium diagnosis. <em>J Am Acad Dermatol.<\/em> 2000.<\/li>\n\n\n\n<li>Messenger AG. Hair cycle disorders. <em>Clin Dermatol.<\/em> 2013.<\/li>\n\n\n\n<li>Sinclair R. Diffuse alopecia mechanisms. <em>Australas J Dermatol.<\/em> 2015.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Abstract Coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2, is associated with a broad spectrum of post-infectious dermatologic sequelae, among which diffuse hair loss\u2014most commonly telogen effluvium (TE)\u2014is increasingly recognized. Hair [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":14912,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-14879","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/posts\/14879","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=14879"}],"version-history":[{"count":2,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/posts\/14879\/revisions"}],"predecessor-version":[{"id":14913,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/posts\/14879\/revisions\/14913"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=\/wp\/v2\/media\/14912"}],"wp:attachment":[{"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14879"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14879"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cov19longhaulfoundation.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14879"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}