TABLE 1.

Main characteristics of the included observational studies in the scoping reviews

Author Year Country	Study Type	Aim	Outcome	Population	Comparative groups	Detail of hair loss	Key findings	Limitations
Abrantes et al. 2021 USA	Observational	To evaluate the onset and duration of acute TE post‐COVID‐19	Investigational	Patients with hair loss after COVID‐19 (n = 30)	N/A	The onset of acute TE at a median of 45 days (IQR 13 days) The median duration of TE was 47.5 days (IQR 45 days) 20/30 (66.7%) had resolution of TE during the follow‐up (March to July 2020)	Acute TE after COVID‐19 could occur sooner than TE of other causes (3 to 6 months to recover)	Small sample size Potential other concomitant causes
Aksoy et al. 2021 Turley	Prospective case–control	To assess the incidence of TE developed following COVID‐19 and the correlation between the development of TE and the severity of infection	Characteristics of hair loss	Patients with TE due to COVID‐19 (n = 57)	Patients without TE (n = 147)	The onset of COVID‐19‐associated TE was an average 53.8 ± 23.8 days after PCR positivity	TE more frequently occurred in those required hospitalization due to COVID‐19 (31.7% vs. 24.3%, p = 0.238) The proportion of women was significantly higher in patients with COVID‐19‐associated TE than men (42.3% vs. 6.2%, p < 0.001) No changes in the extent of stress among those with TE and without TE	The authors did not use objective methods such as trichogram or modified wash test for TE diagnosis No recorded information about trichodynia No long‐term follow‐up to evaluate the recovery
Babaei 2021 Iran	Cross‐sectional	To evaluate the characteristics of TE in COVID‐19	Investigational	526 patients with documented TE that recovered from COVID‐19	N/A	The onset of hair loss was an average 53.6 ± 12.2 days after COVID‐19 27.9% had concurrent alopecia (78.2% androgenic, 19.0% alopecia areata, 2.7% cicatricial alopecia)	8.4%, 7.2%, and 4.8% had concurrent vitamin D deficiency, hypothyroidism, and iron‐deficiency anemia, respectively	Lack of description about recovery Failure to exclude other potential causes of hair loss Cross‐sectional design
Cline 2021 USA	Observational	To evaluate the prevalence of TE pre‐ and during COVID‐19 pandemic	Description of race, ethnicity, and comorbidities of patients with TE	Patients evaluated by the dermatology departments of eight safety‐net hospitals in New York City during the pandemic; from March 1 to October 1, 2020 (n = 14 827)	Patients evaluated by the dermatology departments of eight safety‐net hospitals in New York City pre‐pandemic; from August 1, 2019 to February 29, 2020 (n = 15 507)	39 patients had TE pre‐pandemic and 108 had TE during the pandemic Among 108 patients, 10 had positive COVID‐19. Those with positive COVID‐19 were more likely to have extensive comorbidities and be Hispanic. All of them were female	Those who had TE during the pandemic were more likely to be Hispanic (1.22% vs. 0.30%)	Lack of follow‐up Lack of data about time course after COVID‐19 diagnosis and the onset of hair loss
Di Landro 2021 Italy	Observational	To describe characteristic of TE after COVID‐19	Pathobiology of hair loss in TE after COVID‐19	39 patients with TE after COVID‐19	N/A	The onset of hair loss ranged from 8 weeks to 3 months after clinical manifestation of COVID‐19 7/39 (17.9%) patients had trichodynia The presence of empty follicular ostia and telogen club hairs visible on the scalp surface were noted in 3/39 patients Recovery occurred in 2–4 months	Mean age 64.4 years (range: 48–73) 30/39 (76.9%) patients were female 16/39 (41.0%) required hospitalization due to COVID‐19	Small sample size No description about mean/median time to the onset or recovery of hair loss
Kim 2021 Korea	Retrospective cohort	To investigate the risk of developing alopecia areata among COVID‐19 patients	New diagnosis of alopecia areata based on ICD‐10‐Code L63	7958 patients with COVID‐19 during the study period (January 1 to June 4, 2020)	218 779 patients without COVID‐19 during the study period	18/7958 (0.2%) with COVID‐19 and 195/218584 (0.1%) had alopecia areata based on ICD‐10‐Code	The adjusted incidence rate ratio of developing alopecia areata using a log‐link Poisson regression model was 0.60 (95% CI: 0.35–1.03) in those with COVID‐19 compared with those without COVID‐19	Lack of detailed time course and description concerning hair loss Low prevalence of COVID‐19 in the study area during the period Diagnosis of alopecia areata was based on ICD‐10‐Code
Moreno‐Arrones 2021 Spain	Observational	To characterize acute TE after COVID‐19	Investigational	191 patients with acute TE and prior diagnosis of COVID‐19	N/A	The onset of COVID‐19‐associated TE was an average 57.1 ± 18.3 days after COVID‐19 diagnosis Severity of hair loss based on Sinclair score; 4.7% had a score of 1, 10.5% of 2, 12.6 of 3, 20.4% of 4, 22% of 5, and 29.8% of 6 27.2% recovered within 4 weeks	78.5% female with mean age of 47.4 years (range: 15–88) 71.2% of the patients did not require hospitalization 59.7% received any form of minoxidil for acute TE treatment	Small sample size with lack of long‐term follow‐up
Sharquie 2021 Iraq	Cross‐sectional	To characterize acute TE after COVID‐19	Investigational	39 patients with acute TE after COVID‐19	N/A	All patients experienced hair loss within 2–3 months after COVID‐19 The pull tests were strongly positive (> 10–50% with a mean of 35% of pulled hair away from scalp) in every patient 43.6% had the diffuse type, 30.8% bitemporal type, 12.8% occipital, 7.7% frontovertical, and 5.1% bitemporo‐frontal	No patients required hospitalization for COVID‐19 Mean age 41.3 ± 11.6 years 92.3% females No patients had alopecic patches or scaling, erythema, or other dermatological abnormalities	Small sample size at a single‐center design No description about recovery Lack of a comparison group
Starace 2021 Italy	Cross‐sectional	To evaluate the presence of trichodynia and TE in patients with COVID‐19	Investigational	128 patients with TE and/or trichodynia with a prior history of COVID‐19	N/A	The authors could collect detailed data of 101 patients In patients with trichodynia without TE, TR occurred in 2 weeks (IQR 1–3) after COVID‐19 Those with TE without trichodynia had TE 13 weeks (IQR 10.5–13.2) after COVID‐19 Those with both TE and TR had TE in 3 weeks after COVID‐19 (IQR 2–7.5) Complete resolution of TE or trichodynia occurred in 91/101 (90.1%)	Patients who had anosmia and headache had higher odds of having trichodynia without TE (OR 6.7 and 6.3, respectively)	Survey‐based design causing selection bias Only those who came to dermatology clinic were included Lack of a control group

Abbreviations: COVID‐19, coronavirus disease 2019; ICD, International Classification of Diseases; IQR, interquartile range; OR, odds ratio; TE, telogen effluvium.