Key Points
Question
What is the prevalence of alopecia areata (AA) and its subtypes overall and among racial and ethnic subgroups in the US?
Findings
In this cross-sectional study, 1812 of the 1 093 176 eligible patients had at least 1 code for AA; overall age- and sex-standardized prevalences among adults, children, and adolescents were observed to be 0.18% and 0.10%, respectively. Relative to White patients, standardized prevalence ratios for Asian, Black, and Hispanic/Latino patients were 2.47, 1.35, and 1.26, respectively; cases of alopecia totalis and alopecia universalis comprised approximately 9% of patients diagnosed with AA.
Meaning
The findings of this study suggest that Americans, particularly persons of color, have a significant burden of alopecia areata.
This cross-sectional study examines the prevalence of alopecia areata, alopecia totalis, and alopecia universalis overall and among racial and ethnic groups in the US.
Abstract
Importance
Prevalences of alopecia areata (AA), alopecia totalis (AT), and alopecia universalis (AU) are poorly established.
Objective
To estimate overall and subgroup prevalences of AA and its subtypes.
Design, Setting, and Participants
This cross-sectional study using electronic records comprising the Explorys database (Watson Health, IBM Corporation) included children, adolescents, and adults seeking healthcare across the 4 census regions in the US between January 1, 2019, and December 31, 2019. The statistical analysis was conducted between July 21, 2022, and December 22, 2022.
Main Outcomes and Measures
Prevalent cases of AA, AT, and AU.
Results
Of the 1 093 176 patients who met inclusion criteria, 1812 had at least 1 code for AA, 1216 female (67%) and 596 male (33%) patients. Overall age-and-sex standardized prevalences among adults and among children and adolescents were observed to be 0.18% and 0.10%, respectively. The age-standardized prevalence ratio in women to men was 1.32. Standardized prevalence was highest in those aged 30 to 39 (297 per 100 000; 95% CI, 263-335) and 40 to 49 (270 per 100 000; 95% CI, 240-303) years. The highest standardized prevalence was observed among Asian patients (414 per 100 000; 95% CI, 306-548), followed by patients reporting another race or multiple races (314 per 100 000; 95% CI, 266-368), Black (226 per 100 000; 95% CI, 199-255), and Hispanic/Latino (212 per 100 000; 95% CI, 129-328) patients. White patients had the lowest standardized prevalence (168 per 100 000; 95% CI, 157-179) among racial and ethnic subgroups. Relative to White patients, standardized prevalence ratios for Asian, Black, and Hispanic/Latino patients were 2.47 (95% CI, 2.17-2.81), 1.35 (95% CI, 1.26-1.44), and 1.26 (95% CI, 1.03-1.55), respectively. Cases of AT and AU comprised approximately 9% of patients diagnosed with AA.
Conclusions and Relevance
The findings of this cross-sectional study suggest that there is a significant burden of AA, AT, and AU in the US in which people of color, particularly Asian Americans, appear to be disproportionately affected.
Introduction
Alopecia areata (AA) is an inflammatory disease of the follicular unit that results in nonscarring patches.1,2 Circumscribed patches of hair loss occur most commonly on the scalp, eyebrows, eyelashes, and beard area, although any hair-bearing surface area may be involved. Alopecia areata resulting in complete loss of scalp or total body hair is referred to as alopecia totalis (AT) or alopecia universalis (AU), respectively. Although AA is generally asymptomatic, hair loss due to AA results in significant effects on quality of life.3,4,5,6 Alopecia areata has also been linked to increased risk of mood disorders including anxiety and depression.7,8
Information on overall prevalence of AA and its subtypes in the US is limited, even more so as it relates to disease burden among demographic subgroups. The purpose of this study was to estimate overall prevalence of AA in the health care seeking population, as well as in specific demographic groups in the US. We also aimed to estimate overall and subgroup prevalence of AT and AU.
Methods
This was a cross-sectional study of the Explorys database (Watson Health, IBM Corporation), a multihealth system research platform comprising electronic medical record data from over 40 health care organizations, 400 000 health care professionals, and approximately 53 million unique patients across all 4 census regions in the US.9 Participating institutions largely include hospital systems and integrated health care delivery networks. A 15% random sample of all patients was used in the present analysis. The study population consisted of patients with at least 1 health care encounter at a participating institution in 2019, and at least 90 days of observable person-time between January 1, 2019, and December 31, 2019. Patients were considered “observable” from the date of their first to their last observed encounter in the database.10 The year 2019 was selected as the period of interest for analysis because there were reduced interactions with health care professionals for routine care during the COVID-19 pandemic in 2020. Eligible patients must also have been observable in the database between January 1, 2018, and December 31, 2018, to ensure adequate time for prevalent conditions to be recorded. Individuals with missing sex or age information (approximately 1.5% of patients) were excluded. Overall AA cases (any subtype) were identified based on at least 1 recorded International Classification of Diseases, Ninth Revision (ICD-9) or Tenth Revision (ICD-10) code (704.01, or L63.x), occurring at any time in the patient’s medical record. Cases of AT and AU were identified based on at least 1 record of ICD-10 codes L63.0 and L63.1, respectively. This case identification method was found to have a positive predictive value of 89% for overall AA, 64% for AT, and 86% for AU.11 The composite outcome of AT or AU was analyzed in the primary analysis given small numbers of patients with each individual diagnosis, particularly within subgroups. In a sensitivity analysis, we defined prevalent cases of AA (any subtype) according to at least 2 ICD-9 or ICD-10 codes.
Prevalence was calculated as the number of patients meeting the case definition(s) divided by the total number of eligible patients during the study period. Crude and standardized prevalences of each outcome were calculated for the overall sample as well as subgroups stratified by age, sex, and race. Direct standardization, based on population estimates from the 2019 American Community Survey,12 was used to facilitate comparison across groups while accounting for differences in age and sex distributions. Confidence intervals for crude and standardized prevalences were based on the normal and gamma distributions, respectively.13 To provide further context into potential differences in AA prevalence across racial or ethnic subgroups, we performed an exploratory analysis comparing prevalence in those with Medicaid vs non-Medicaid insurance, stratified by race. This analysis was also adjusted for age using direct standardization. This study was approved by the human participants committee at the Feinstein Institutes for Medical Research at Northwell Health and written informed consent was waived because all data used were deidentified.
Results
Overall Alopecia Areata
A total of 1 093 176 patients met criteria for inclusion, among whom 1812 had at least 1 code for AA. This yielded an overall crude prevalence of 0.17%, or 166 per 100 000 (95% CI, 158-173). Age- and sex-standardized overall prevalence was 0.18%, or 176 per 100 000 (95% CI, 168-185) (Table 1). Among pediatric patients aged 0 to 17 years, sex-standardized prevalence was 0.10%, or 104 per 100 000 (95% CI, 92-116). Age-standardized prevalence in females and males were 198 (95% CI, 187-210) and 151 (95% CI, 138-164) per 100 000, respectively, which corresponded to a prevalence ratio of 1.32 (95% CI, 1.19-1.46). Standardized prevalence increased with advancing age groups up to ages 30 to 39 (297 per 100 000) years and 40 to 49 (270 per 100 000) years, and then it followed a decreasing trend for older age groups.
Table 1. Overall and Demographic Subgroup Prevalence of Alopecia Areata.
| Group | Alopecia areata cases, all types | Total patients | Prevalence, % | Crude prevalence per 100 000 (95% CI) | Standardized prevalence per 100 000 (95% CI)a |
|---|---|---|---|---|---|
| Overall | 1812 | 1 093 176 | 0.17 | 166 (158-173) | 176 (168-185) |
| Sex | |||||
| Female | 1216 | 621 033 | 0.20 | 196 (185-207) | 198 (187-210) |
| Male | 596 | 472 143 | 0.13 | 126 (116-136) | 151 (138-164) |
| Age group, y | |||||
| 0-17 (pediatric) | 284 | 274 935 | 0.10 | 103 (91-115) | 104 (92-116) |
| 0-9 | 105 | 142 026 | 0.07 | 74 (60-88) | 75 (61-90) |
| 10-17 | 179 | 132 909 | 0.13 | 135 (115-154) | 135 (116-156) |
| ≥18 (adult) | 1528 | 818 241 | 0.19 | 187 (177-196) | 180 (171-189) |
| 18-29 | 237 | 145 833 | 0.16 | 163 (141-183) | 162 (142-185) |
| 30-39 | 293 | 103 009 | 0.28 | 284 (252-317) | 297 (263-335) |
| 40-49 | 301 | 108 465 | 0.28 | 278 (246-309) | 270 (240-303) |
| 50-59 | 251 | 137 260 | 0.18 | 183 (160-205) | 174 (153-197) |
| 60-69 | 246 | 150 446 | 0.16 | 164 (143-184) | 154 (136-175) |
| 70-79 | 162 | 110 082 | 0.15 | 147 (125-170) | 138 (117-160) |
| 80-89 | 38 | 63 146 | 0.06 | 60 (41-79) | 54 (38-74) |
| Race and ethnicityb | |||||
| Asian | 54 | 13 234 | 0.41 | 408 (299-517) | 414 (306-548) |
| Black | 269 | 120 032 | 0.22 | 224 (197-251) | 226 (199-255) |
| Hispanic/Latino | 20 | 9665 | 0.21 | 207 (116-298) | 212 (129-328) |
| White | 1009 | 619 464 | 0.16 | 163 (153-173) | 168 (157-179) |
| Other/multiracialc | 153 | 50 743 | 0.30 | 302 (254-349) | 314 (266-368) |
Overall prevalence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific prevalences are standardized by age. Age-specific prevalences are standardized by sex. Prevalences specific to race and ethnicity are standardized by age.
280 038 patients were missing race and ethnicity. Patients missing race and ethnicity were included in the estimates of AA prevalence for the overall group, and sex and age subgroups.
Comprised of Asian/Pacific Islander, Native American or Alaska Native, Native Hawaiian, multiracial, or other (not specified).
Crude and standardized prevalence according to patient-reported race and ethnicity is also presented in Table 1. The highest standardized prevalence was observed among Asian patients (414 per 100 000; 95% CI, 307-548), followed by patients reporting an other race or multiple races (314 per 100 000; 95% CI, 266-368), Black (226 per 100 000; 95% CI, 199-255), and Hispanic/Latino (212 per 100 000; 95% CI, 129-328) patients. White patients had the lowest standardized prevalence (168 per 100 000; 95% CI, 157-179) among racial subgroups. Relative to White patients, standardize prevalence ratios for Asian, Black, and Hispanic/Latino patients were 2.47 (95% CI, 2.17-2.81), 1.35 (95% CI, 1.26-1.44), and 1.26 (95% CI, 1.03-1.55), respectively (Table 2).
Table 2. Prevalence Ratios for Alopecia Areata, Alopecia Totalis, and Alopecia Universalis by Age, Sex, and Race and Ethnicity.
| Comparison group | Standardized prevalence ratio (95% CI)a | ||
|---|---|---|---|
| Alopecia areata (all types) | Alopecia totalis/alopecia universalis (combined) | ||
| >1 diagnosis | >2 diagnoses | ||
| Sex | |||
| Female | 1.32 (1.19-1.46) | 1.30 (1.11-1.52) | 2.63 (1.74-3.97) |
| Male | 1 [Reference] | 1 [Reference] | 1 [Reference] |
| Age, y | |||
| Adult (≥18) | 1.73 (1.53-1.97) | 2.26 (1.82-2.81) | 1.47 (0.94-2.28) |
| Pediatric (0-17) | 1 [Reference] | 1 [Reference] | 1 [Reference] |
| Race and ethnicity | |||
| Asian | 2.47 (2.17-2.81) | 3.10 (2.61-3.68) | NAb |
| Black | 1.35 (1.26-1.44) | 1.18 (1.07-1.32) | NAb |
| Hispanic/Latino | 1.26 (1.03-1.55) | NAb | NAb |
| White | 1 [Reference] | 1 [Reference] | |
| Other/multiracial | 1.87 (1.72-2.03) | 1.83 (1.62-2.06) | NAb |
Abbreviation: NA, not applicable.
Confidence intervals for standardized prevalence ratios are based on the lognormal distribution.
Prevalence ratios were not computed due to the small number of cases within the subgroup. Standardized prevalence ratio is based on 10 AT cases in the subgroup of Black patients, and should be interpreted cautiously.
In an exploratory analysis, age-adjusted AA prevalence did not differ significantly between patients with Medicaid and non-Medicaid insurance in any racial subgroup (prevalence ratio in Black patients, 1.16; 95% CI, 0.86-1.58; White patients, 0.96; 95% CI, 0.78-1.18; other/multiracial patients [Asian/Pacific Islander, Native American or Alaska Native, Native Hawaiian, multiracial, or other not specified], 0.89; 95% CI, 0.60-1.31; eTable 1 in Supplement 1).
In a sensitivity analysis requiring at least 2 AA diagnosis codes, crude prevalence was reduced to 70 per 100 000 (95% CI, 65-74). Patterns across demographic subgroups, including age trends and prevalences ratios, were similar to the primary analysis (Table 2; eTable 2 in Supplement 1).
Among 1507 patients with at least 1 ICD-10 code for AA, in which subtype could be specified, 139 patients (9.2%) were diagnosed with AT or AU.
Alopecia Totalis or AU
Crude prevalence of AT or AU was 0.02%, or 12.7 (95% CI, 10.6-14.8) per 100 000 (Table 3). Standardized prevalence per 100 000 was 12.9 (95% CI, 10.6-15.5) among adults aged 18 years or older, and 8.8 (95% CI, 5.6-13.1) among children and adolescents aged 0 to 17 years, which resulted in a prevalence ratio of 1.47 (95% CI, 0.94-2.28). Age-standardized prevalences in female and male patients were 16.4 (95% CI, 13.4-19.9) and 6.3 (95% CI, 4.2-9.0) per 100 000, respectively, which resulted in a prevalence ratio of 2.63 (95% CI, 1.74-3.97) (Table 2). Crude prevalence generally increased with advancing age. Results of exploratory analyses of the prevalence of AT and AU individually are presented in eTables 3 and 4 in Supplement 1.
Table 3. Overall and Subgroup Prevalence of Alopecia Totalis or Alopecia Universalis.
| Group | Alopecia totalis/universalis cases (either) | Total patients | Prevalence, % | Crude prevalence per 100 000 (95% CI) | Standardized prevalence per 100 000 (95% CI)a |
|---|---|---|---|---|---|
| Overall | 139 | 1 093 176 | 0.01 | 12.7 (10.6-14.8) | 11.6 (9.7-13.8) |
| Sex | |||||
| Female | 108 | 621 033 | 0.02 | 17.4 (14.1-20.7) | 16.4 (13.4-19.9) |
| Male | 31 | 472 143 | 0.01 | 6.6 (4.3-8.9) | 6.3 (4.2-9.0) |
| Age group, y | |||||
| 0-17 (pediatric) | 24 | 274 935 | 0.01 | 8.7 (5.2-12.2) | 8.8 (5.6-13.1) |
| ≥18 (adult) | 115 | 818 241 | 0.01 | 14.1 (11.5-16.6) | 12.9 (10.6-15.5) |
| 18-44 | 28 | 300 959 | 0.009 | 9.3 (5.9-12.7) | 8.7 (5.7-12.7) |
| 45-64 | 43 | 270 041 | 0.02 | 15.9 (11.2-20.7) | 14.6 (10.6-19.8) |
| ≥65 | 44 | 247 241 | 0.02 | 17.8 (12.5-23.1) | 16.4 (11.9-22.0) |
Overall prevalence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific prevalences are standardized by age. Age-specific prevalences are standardized by sex.
Discussion
In a large cohort of patients with AA in the US, we have estimated overall age- and sex-standardized prevalence to be 0.18% and 0.10% in adults and in children and adolescents, respectively. Highest prevalences of AA were observed among patients aged 30 to 39 years and 40 to 49 years. Prevalence of AA in women was 1.3 times that of men. In addition, we observed a disproportionate burden of AA among Asian patients. Alopecia areata was also more prevalent among Black and Hispanic patients than in White patients.
Cases of AT and AU comprised approximately 9% of patients diagnosed with AA. Prevalence trends observed in these subtypes were generally consistent with those for overall AA. Prevalence of AT or AU combined was higher in women. The composite of AT or AU was also more common in adults than in children and adolescents, though the CI for this comparison was wide and included the null value of 1. The small number of cases prevented meaningful comparison of the AA subtypes across race and ethnic groups.
Few population-based studies explore overall and subgroup prevalences of AA in the US. Information on AA prevalence among demographic subgroups is further limited. These studies are limited by self-report of diagnosis, selected cases (ie, only female participants) or controls, and restriction of subgroup analysis due to low case counts, which reduces generalizability to the broader population in the US. Data from the First National Health and Nutrition Examination Survey (NHANES) in the early 1970s estimated the overall AA prevalence to be 0.12%.14 Prevalences for demographic subgroups were not provided, likely owing to the small number of cases. In a cross-sectional study, prevalence of AA was estimated to be 1.1% based on self-reports from a questionnaire administered online. The prevalence was reduced to 0.2% after clinician adjudication by photograph from a sample of patients.15 Self-reported AA prevalence was 2.5, 2.0, and 2.2 times as high among Asian, Black, and Hispanic patients compared with White patients. The prevalence ratio for female relative to male patients based on self-report was 0.69. Authors acknowledged the difficulty patients had in distinguishing AA from androgenic alopecia, and it is possible that men with the latter were more likely to self-report diagnosis of AA. In an electronic record-based study evaluating AA prevalence in pediatric patients across 5 children’s hospitals in the US between 2009 and 2020, prevalence was observed to be 0.11%.16 The female to male prevalence ratio was 1.32. Hispanic, Asian, and Black children and adolescents had prevalence ratios of 2.93, 2.16, and 1.59, respectively, relative to White patients.16 In the Nurses’ Health Studies in which women self-reported AA diagnosis, prevelances were observed to be 0.65% and 0.84%. Black and Hispanic female participants reported higher prevalences of AA compared with White participants.17 In a case-control study from the National Alopecia Areata Registry (NAAR), Black patients had higher odds of having AA compared with White patients, although Asian and Hispanic patients had lower odds of AA compared with White patients.18 Results of this analysis are likely subject to selection bias because control participants were not identified from the same source population as the participants in the AA cases group, but rather included volunteers from the NAAR research team, those identified at alopecia-related conferences, and those identified through internet advertisements.
Information on burden of AT and AU, particularly within demographic subgroups, is also limited. In the online survey study cited previously, 4 of 19 patients with AA were clinician-adjudicated as having AT or AU, which resulted in a population prevalence of 0.04% for combined AT and AU.15 In a recent analysis of the IBM MarketScan insurance claims database, 8.3% of adults with AA were diagnosed with AT or AU.19 Three of 26 total patients with AA identified in the first NHANES survey in the United States were diagnosed as having AT or AU.14
Limitations
There are limitations to our analysis that merit consideration. We could not capture patients with AA who went undiagnosed or those who did not seek care in health systems included in the database. This study may have overrepresented cases of severe AA because those patients are more likely to seek care. The composition of the Explorys database, largely comprising integrated health care networks and academic medical centers, may also overrepresent severe forms of AA because patients with AT and AU are more likely to be referred to these care settings. However, the percentage of AT or AU cases in the present analysis (9.2%) was not markedly different from a recent insurance claims-based analysis (8.3%), which included cases diagnosed across a range of health care settings. Lastly, there was variation in the overall AA prevalence estimate according to case definition (1 vs 2 diagnoses). Results from the sensitivity analysis can be interpreted as a lower bound on the overall prevalence estimate. Advantages of the present study include the large sample size, cohort diversity, and standardization of prevalence estimates using 18 age- and sex-specific strata, all of which strengthen generalizability. We also provide detailed estimates of alopecia areata subtype prevalence according to age and sex.
Conclusions
There is a significant burden of AA in the US in which people of color, particularly Asian Americans, appear to be disproportionately affected. In aggregate AT and AU appear to represent almost 10% of patients diagnosed with AA.
eTable 1. Age-adjusted prevalence of any alopecia areata (all subtypes) per 100 000 according to racea and Medicaid insurance status
eTable 2. Sensitivity analysis of overall and demographic subgroup alopecia areata prevalence based on at least 2 diagnosis codes
eTable 3. Overall and demographic subgroup prevalences of alopecia totalis
eTable 4. Overall and demographic subgroup prevalences of alopecia universalis
Data Sharing Statement
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eTable 1. Age-adjusted prevalence of any alopecia areata (all subtypes) per 100 000 according to racea and Medicaid insurance status
eTable 2. Sensitivity analysis of overall and demographic subgroup alopecia areata prevalence based on at least 2 diagnosis codes
eTable 3. Overall and demographic subgroup prevalences of alopecia totalis
eTable 4. Overall and demographic subgroup prevalences of alopecia universalis
Data Sharing Statement