Key Points
Question
What is the prevalence of psoriasis in adults in the US, and how has prevalence changed since 2003?
Findings
In this nationally representative cross-sectional study including 12 625 participants, the prevalence of psoriasis in adults in the US was 3.0%, indicating that more than 7.5 million adults 20 years or older have psoriasis. Psoriasis was most common in non-Hispanic White individuals, and the prevalence of psoriasis has not significantly changed since 2003 in the US.
Meaning
Study results suggest that psoriasis remains one of the most common immune-mediated diseases affecting US adults; prevalence data are foundational to determining the burden of disease.
This cross-sectional study uses data from the National Health and Nutrition Examination Survey to assess the prevalence of psoriasis in adults in the US and how it has changed since 2003.
Abstract
Importance
Determining psoriasis prevalence is fundamental to understanding the burden of the disease, the populations most affected, and health policies to address the disease.
Objective
(1) To determine the prevalence of psoriasis among adults in the US and (2) to evaluate the change in psoriasis prevalence over time since the 2003-2004 National Health and Nutrition Examination Survey (NHANES) data.
Design, Setting, and Participants
This population-based cross-sectional study used 2011-2014 NHANES data (collected from January 1, 2011, to December 31, 2014) with sampling from a general, noninstitutionalized US civilian population. Participants were 20 years or older and were selected via a multistage probability sampling design to ensure that surveys were nationally representative. Eligible participants had an in-person interview followed by a medical examination by medical professionals. Data were analyzed from July 15, 2019, to December 23, 2020.
Exposures
None.
Main Outcomes and Measures
Psoriasis prevalence in the US, as measured by the percentage of people in the representative sample with psoriasis, and trend statistics comparing prevalence estimates from the 2003-2004, 2009-2010, and 2011-2014 NHANES cycles.
Results
A total of 12 625 participants (mean [SD] age, 32.8 [24.1] years; 6492 women [51.4%]; and 4828 non-Hispanic White participants [38.2%]) answered the question of whether they were given the diagnosis of psoriasis by a physician or another health care professional. Psoriasis prevalence among US adults 20 years or older was 3.0% (95% CI, 2.6%-3.4%). Based on the 2020 US census data, this outcome translates to an estimated 7.55 million US adults with psoriasis. Psoriasis prevalence was similar between women and men, with 3.2% (95% CI, 2.6%-3.8%) in women and 2.8% (95% CI, 2.4%-3.3%) in men. Psoriasis prevalence was highest in White individuals at 3.6% (95% CI, 2.9%-4.2%), followed by other racial/ethnic groups (non-Hispanic, including multiracial) at 3.1% (95% CI, 1.2%-5.1%), Asian individuals at 2.5% (95% CI, 1.6%-3.3%), Hispanic individuals (including Mexican American and other Hispanic individuals) at 1.9% (95% CI, 1.3%-2.5%), and Black individuals at 1.5% (95% CI, 1.0%-2.0%). Psoriasis prevalence was not different based on patients’ marital status, education, income, or medical insurance status. The prevalence of psoriasis among US adults did not differ significantly since 2003.
Conclusions and Relevance
The results of this cross-sectional study suggest that psoriasis remains a common, immune-mediated disease that affects 3.0% of the US adult population, or more than 7.5 million adults. Its prevalence has not differed since evaluation in 2003. These prevalence data are foundational to determining the burden of psoriasis and for supporting efforts in research, education, and health policy.
Introduction
Psoriasis is an immune-mediated skin disease associated with multiple comorbidities, including psoriatic arthritis, cardiometabolic diseases, and mental health conditions.1,2,3,4,5 Psoriasis and its comorbidities can lead to significant decrement in quality of life and incur substantial societal costs.6
Determining the prevalence of psoriasis is critical because such information has several important implications. First, psoriasis prevalence informs clinicians and patients on disease epidemiology and the populations most at risk for having the disease. Second, prevalence data help inform health policies on allocation of health care resources. Third, such data establish baseline population estimates for subsequent studies evaluating subpopulations.
The prevalence of psoriasis varies across the world.7,8,9,10,11,12,13,14,15,16,17,18 Systematic reviews have shown that psoriasis prevalence in children ranges from 0% in Taiwan to approximately 2.1% in Italy and that the rates among adults vary from 0.4% in Asian countries to 8.5% in Norway.
Previous studies of psoriasis prevalence in the US have reported varied data depending on the population of interest, methodology, and data source.19,20,21,22,23 Prior work has found the prevalence of psoriasis for US adults to be 3.2%.20,22 A lower prevalence of 1.23% (95% CI, 1.20%-1.25%) had been reported in an older population using a sample from the US Medicare beneficiary database.23 In children younger than 18 years, insurance billing databases showed a psoriasis prevalence of 0.128% (95% CI, 0.124%-0.131%).21 In general, investigators using databases that focused on urban or commercially insured populations experienced challenges collecting data from rural and underserved populations.
The National Health and Nutrition Examination Survey (NHANES) is a survey designed to assess the health of adults and children in the US by using a nationally representative sample. This national survey oversamples Black, Hispanic, and low-income White patients to ensure improved capture of disease burden in these populations. Recently, Liu et al24 examined the 2013-2014 NHANES cycle and determined psoriasis prevalence for adults to be 2.8%; this study advanced our understanding of the overall prevalence of psoriasis among adults based on a 2-year national survey.
In this study, we aimed (1) to determine the up-to-date prevalence of psoriasis among adults in the US using NHANES and (2) to evaluate the change in psoriasis prevalence over time among adults aged 20 to 59 years through a comparison with prior NHANES findings. The current study builds on and extends the findings by Liu et al24 in 3 ways. First, per the Centers for Disease Control and Prevention (CDC) recommendations, we combined multiple NHANES cycles and thereby doubled the sample size.25 This method resulted in prevalence estimates with high precision, accuracy, and stability, not only for the overall population but also for the demographic subgroups. In addition, we characterized psoriasis severity from the 2011-2012 and 2013-2014 NHANES cycles. Last, we extended the comparison of the present prevalence rates to earlier prevalence data dating back to 2003.
Methods
Study Design
The cross-sectional data from NHANES are released biennially by the National Center for Health Statistics (NCHS), which is a branch of the CDC. Every released survey cycle consists of 2 years of health examination data from a nationally representative sample of a noninstitutionalized US civilian population.25 The CDC/NCHS recommends its use to estimate the prevalence of various diseases,26 and NHANES data have been used for this purpose frequently over the past 2 decades across many medical fields.27,28,29
The CDC/NCHS recommend that researchers combine NHANES cycles into samples of 4 years (2 cycles) “whenever possible to improve statistical reliability and stability of prevalence estimates.”25(p8) In accordance with this recommendation, for this cross-sectional study, we calculated the prevalence of psoriasis in the US from 2 NHANES cycles (4 years)—specifically, the 2011-2012 and 2013-2014 cycles—because they contained the latest data on psoriasis prevalence. Because the NHANES protocols and sampling methods are identical between the 2011-2012 and 2013-2014 cycles, we were able to merge the 2 data sets into 1 larger data set. From this larger data set, we could calculate the prevalence of psoriasis by dividing the number of participants who reported having been diagnosed with psoriasis by a physician or another health care professional by the total number of participants who responded to the psoriasis question. The NHANES surveys were approved by the NCHS Research Ethics Review Board (Protocol No. 2011-17). This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines.
Study Population
A multistage stratification with 4 different levels was used to choose participants. To achieve a sample that was representative of the noninstitutionalized US civilian public, the NCHS oversampled Black, Hispanic, Asian, and non-Hispanic adults 80 years and older and White Americans with low income (at or below 130% of the federal poverty line) for the 2011-2014 cycles.
After this multistage selection process, eligible survey participants completed a health survey questionnaire via interview followed by an in-person physical examination by medical personnel.25 Skin examinations are generally not performed for NHANES except during the 2003-2004 cycle.30 Questions about the diagnosis and severity of psoriasis were asked of all survey participants 20 years and older.
A total of 12 638 people participated in the psoriasis question (unweighted sample), with 12 625 giving a definitive yes or no answer from the combined 2011-2014 NHANES data. Among them, a total of 329 people answered the question on psoriasis severity. Specifically, in the 2011-2012 data set, 6174 people participated in the psoriasis question, with 6167 providing a definitive yes or no answer. In the 2013-2014 data set, 6464 people participated in the psoriasis question, with 6458 providing a definitive yes or no answer.
Demographic information was also collected for each participant, including race/ethnicity, age, sex, income, education, marital status, and insurance status (Table 1). Race/ethnicity was divided into the following categories: White (non-Hispanic, single race); Black (non-Hispanic, single race); Asian (non-Hispanic, single race); other (non-Hispanic, including multiracial persons); and Hispanic (Hispanic–Mexican American and other Hispanic). Throughout this article, we have used the same terminology for racial/ethnic groups as was used by NHANES.
Table 1. Comparison of Demographic Factors Between Patients With and Without Psoriasis.
| Demographic factor | % (95% CI) | |
|---|---|---|
| No psoriasis | Psoriasis | |
| Male | 48.1 (47.0-49.1) | 45.2 (39.3-51.2) |
| Female | 51.9 (50.9-53.0) | 54.8 (48.8-60.7) |
| Age, mean (95% CI), y | 47.3 (46.4-48.2) | 50.8 (48.3-53.2) |
| Race/ethnicity | ||
| Non-Hispanic White | 65.7 (60.5-71.0) | 78.0 (72.2-83.7) |
| Non-Hispanic Black | 11.7 (8.8-14.5) | 5.7 (3.1-8.3) |
| Non-Hispanic Asian | 5.3 (4.2-6.4) | 4.3 (2.5-6.1) |
| Hispanic | 14.7 (11.1-18.2) | 9.3 (5.2-13.3) |
| Non-Hispanic other (including multiracial) | 2.6 (2.0-3.2) | 2.7 (1.0-4.5) |
| Income <$45 000/y | 38.8 (35.2-42.4) | 41.4 (33.3-49.5) |
| No advanced education (ie,<high school) | 16.0 (13.7-18.4) | 14.0 (7.4-20.6) |
| Not married | 45.8 (43.0-48.5) | 47.1 (40.7-53.5) |
| No health insurance | 19.1 (17.3-21.0) | 16.7 (11.8-21.7) |
To evaluate trends in psoriasis prevalence over time, we calculated the prevalence among those aged 20 to 59 years from the most recent 2011-2014 NHANES data on psoriasis because the age group with the most consistently captured data over the years are those from ages 20 to 59 years. We then compared that value to the prevalence among those aged 20 to 59 years, which was reported from the prior NHANES cycles of 2009-2010 and 2003-2004.
Questions on Psoriasis and Psoriasis Severity
The NHANES survey asked patients if they had ever been told by a doctor or other health care professional that they had psoriasis. The participating respondents could answer “yes,” “no,” or “don’t know.” Different from prior NHANES cycles, the 2011-2014 data sets also included a question on the degree of psoriasis. Those surveyed were asked if they “currently have…” and could choose from “little or no psoriasis,” “only a few patches (that could be covered by 1 or 2 palms of your hand),” “scattered patches (that could be covered between 3 and 10 palms of your hand),” “extensive psoriasis (covering large areas of the body that would be more than 10 palms of your hand),” or “don’t know.”
Statistical Methods
We used R software, version 3.5.0 (R Foundation) to conduct all statistical analyses.30 To allow inference to the general population, we used the survey library to incorporate the appropriate sample weights and adjust for clusters and strata of the complex sample design. Responses to the medical questionnaire were used to determine the prevalence rate of psoriasis. Overall prevalence and prevalence adjusted by demographic factors were reported as percentages with 95% CIs. Survey logistic regression for both unadjusted and adjusted (for age and sex) analyses were computed to obtain weighted odds ratios (ORs) with 95% CIs. To compare psoriasis prevalence rates from 2003-2004, 2009-2010, and 2011-2014, the survey-based Rao-Scott corrected Pearson χ2 test was used. A result was considered significant when its 2-sided P value was less than .05. Data were analyzed from July 15, 2019, to December 23, 2020.
Results
A total of 12 625 participants (mean [SD] age, 32.8 [24.1] years; 6492 women [51.4%] and 6133 men [48.6%]; and 4828 non-Hispanic White participants [38.2%]) answered the question on whether they were given the diagnosis of psoriasis by a physician or another health care professional. The prevalence of psoriasis in people 20 years or older was 3.0% (95% CI, 2.6%-3.4%) (Table 2). Based on the prevalence of psoriasis from this study and using the 2020 US census data, that prevalence equates to approximately 7 559 850 people aged 20 years or older having psoriasis.31 Psoriasis prevalence was similar between women and men, with 3.2% (95% CI, 2.6%-3.8%) in women and 2.8% (95% CI, 2.4%-3.3%) in men. A summary of demographic and clinical factors for patients with and without psoriasis is shown in Table 1. Overall, compared with those without psoriasis, patients with psoriasis tended to be older. Specifically, among those aged 20 to 59 years, older age was significantly associated with psoriasis (OR, 1.03; 95% CI, 1.01-1.04) (Table 3). For example, psoriasis prevalence was 1.6% among people aged 20 to 29 years, whereas it was 4.3% among those aged 50 to 59 years (Table 2). Those with and without psoriasis had similar levels of sociodemographic factors such as marital status, education, income, or medical insurance status (Table 1).
Table 2. Demographic and Clinical Factors in Patients 20 Years or Older With Psoriasis in the US.
| Category | Psoriasis prevalence, % (95% CI) |
|---|---|
| Overall | 3.0 (2.6-3.4) |
| Sex | |
| Women | 3.2 (2.6-3.8) |
| Men | 2.8 (2.4-3.3) |
| Age, y | |
| 20-29 | 1.6 (0.9-2.2) |
| 30-39 | 2.9 (2.0-3.8) |
| 40-49 | 3.0 (1.6-4.3) |
| 50-59 | 4.3 (2.8-5.7) |
| 60-69 | 2.7 (1.8-3.7) |
| ≥70 | 3.9 (2.6-5.1) |
| Race/ethnicity | |
| Non-Hispanic White | 3.6 (2.9-4.2) |
| Non-Hispanic Black | 1.5 (1.0-2.0) |
| Non-Hispanic Asian | 2.5 (1.6-3.3) |
| Hispanic | 1.9 (1.3-2.5) |
| Non-Hispanic other (including multiracial) | 3.1 (1.2-5.1) |
| Psoriasis severity | |
| Little or no psoriasis | 56.0 (48.8-63.1) |
| Only a few patches (1-2 palms) | 21.8 (15.0-28.5) |
| Scattered patches (3-10 palms) | 16.0 (9.0-23.0) |
| Extensive psoriasis (>10 palms) | 5.5 (2.3-8.7) |
Table 3. Multivariate Analysis of Factors Associated With Psoriasis Diagnosis Among US Adults Aged 20-59 Years.
| Variable | Odds ratio (95% CI) |
|---|---|
| Age | 1.03 (1.01-1.04) |
| Men vs women | 0.9 (0.64-1.26) |
| White vs non-White | 1.92 (1.28-2.88) |
| Unmarried vs married | 1.14 (0.8-1.63) |
| Not insured vs insured | 1.06 (0.7-1.61) |
| Income <$45 000/y vs ≥$45 000/y | 1.15 (0.75-1.78) |
| Less than HS diploma vs HS diploma or greater | 0.75 (0.46-1.24) |
Abbreviation: HS, high school.
Psoriasis prevalence differed significantly by race/ethnicity (Table 2). NHANES oversamples minority and low-income populations. Overall, White individuals reported the highest prevalence of psoriasis at 3.6% (95% CI, 2.9%-4.2%). The lowest psoriasis prevalence was found in Black individuals, with a prevalence of 1.5% (95% CI, 1.0%-2.0%). Multivariable regression analysis showed that White individuals had nearly twice the odds of having psoriasis (OR, 1.92; 95% CI, 1.28-2.88) compared with non-White individuals after adjusting for age, sex, education, income, marital status, and insurance status (Table 3). Of note, multivariable analyses also showed that psoriasis prevalence was not different based on patients’ marital status, education, income, or medical insurance status (Table 3).
Among the 329 respondents who rated psoriasis severity, a majority (180 [54.7%]) stated they had “little to no” psoriasis at the time of the survey. Another 76 respondents (23.1%) stated they currently had “only a few patches (1-2 palms),” whereas 53 (16.1%) stated they had “scattered patches (3-10 palms).” Last, 16 respondents (4.8%) stated they had “extensive psoriasis (>10 palms),” and 4 respondents (1.2%) stated they “don’t know” the severity of their psoriasis. These percentages are reflective of the unweighted counts; Table 2 represents the weight-corrected population estimates.
The prevalence of psoriasis among those aged 20 to 59 years within the 2011-2014 NHANES data was 2.9% (95% CI, 2.5%-3.4%). This most recent prevalence estimate was not statistically different from prevalence estimates from prior years of 2.9% (95% CI, 2.3%-3.5%) during the 2009-2010 NHANES cycle and 3.2% (95% CI, 2.2%-4.5%) from the 2003-2004 NHANES cycle (P = .84).
Discussion
Based on the prevalence of psoriasis from this study and using the 2020 census data,31 we estimate that more than 7.5 million people aged 20 years or older in the US have psoriasis. This study suggests that psoriasis remains one of the most common immune-mediated diseases experienced by many adults in the US. Determining the prevalence of psoriasis is fundamental, because these data inform and convey its epidemiologic burden to clinicians, patients, researchers, policy makers, and other stakeholders in their efforts to improve the lives of people with this disease. NHANES provides robust data sets for evaluating psoriasis prevalence in the US. Specifically, NHANES uses a multistage, stratified survey methodology to ascertain prevalence data that are representative of the general US adult population. In addition, the oversampling of Black, Hispanic, and low-income White individuals helps improve the accuracy of prevalence estimates among traditionally underrepresented groups in prevalence studies.
Additionally, these data suggest that, compared with those from NHANES over the preceding decade since 2003, psoriasis prevalence through 2014 has not significantly differed in the US.22,32 The relatively stable prevalence in the US differs from the increase in psoriasis prevalence reported in some other countries.8,33,34 The increasing prevalence observed in other countries could be due, at least in part, to the increased recognition of psoriasis or increased life span in these countries. It is unlikely that genetic factors have contributed to the fluctuations in prevalence during the past 30 years, because genetic changes typically take much longer to occur. Although outside the scope of this study, future research in incidence could help clarify differences in temporal trends in psoriasis epidemiology. For example, a combined increased incidence and prevalence would suggest that either changing environmental or lifestyle factors created a true increase in the disease burden or that there is an increased recognition of psoriasis. In comparison, stable incidence with increased prevalence might suggest that patients with psoriasis are living longer. Globally, although some studies found that the incidence of psoriasis has increased over time, others have found it to be stable.8,33,34
In this nationally representative sample of the US population in which racial/ethnic minorities were oversampled, psoriasis prevalence in White patients was nearly double that of non-White patients in the US. These findings are generally consistent with genetic and epidemiologic studies from other parts of the world.35 In the African population, prior studies reported that psoriasis prevalence was higher in Eastern sub-Saharan Africa than in Western sub-Saharan Africa.36,37,38 In the US, many Black individuals report Western sub-Saharan African heritage, and some are from mixed ancestry. Although psoriasis prevalence among Black adults in this study (1.5%) was similar to that reported in prior studies,22,35,36,37 continued research efforts are necessary to determine the precise genetic and environmental contributions to psoriasis pathogenesis in various racial and ethnic groups.
In addition, although oversampling of racial minorities helps mitigate selection bias and create a sample more representative of the US population, other factors that disproportionately affect certain populations may still contribute to the underdiagnosis of psoriasis. A previous study showed that male, non-White, less educated, and/or unmarried individuals were more likely to have undiagnosed psoriasis.32 Other factors leading to underdiagnosis include social determinants of health, such as a lack of access to health care providers due to geographic or economic limitations. For example, in urban areas, many communities of color face barriers in screening, prevention, and treatment of diseases due to decreased access to health care professionals and facilities with accreditation and resources.39,40 Furthermore, cultural preferences may affect one’s health care–seeking behavior and use of health care resources, which may lead to an underestimation of psoriasis prevalence in the aforementioned groups.
These study findings also suggest that in the US, prevalence of psoriasis was similar between men and women and among patients with different education, income, marital, and insurance status after adjustments for other demographic factors.
In this study, we found that 21.5% of participants reported having moderate to severe psoriasis (≥3 palms of body surface area involvement). The majority of patients with psoriasis reported having little or no psoriasis at the time of the survey. It is important to note that the survey does not distinguish between treated vs untreated patients. Thus, a proportion of those reporting low body surface area involvement may be receiving treatments that are controlling their otherwise more extensive disease.
The results from this study appear to confirm the conclusion from Liu et al24 that psoriasis is most common among White individuals and least prevalent among Black individuals in the US. However, the 2 studies yielded different estimates for the different racial/ethnic categories.
This study provided several new findings, because it was based on the CDC’s recommendation of using a sample size that incorporates 2 survey cycles, which resulted in a sample size twice what was previously used.24 First, this study showed that the psoriasis prevalence was 3.0%, which is 0.2% higher than the 2.8% found previously. This 0.2% difference represents approximately 420 000 adult patients with psoriasis. Using 2 NHANES cycles allows for the most accurate and up-to-date estimate of psoriasis prevalence in US adults.
The different samples used in the 2 studies also resulted in important differences within the demographic subgroups. For instance, this study found that the psoriasis prevalence among Black individuals was 1.5% (95% CI, 1.0%-2.0%), compared with 1.0% (95% CI, 0.1%-1.8%) estimated by Liu et al.24 Additionally, this study showed psoriasis prevalence among men to be 2.8% (95% CI, 2.4%-3.3%) compared with 2.5% (95% CI, 1.8%-3.2%).24 Overall, the results from our larger study yielded more precise estimates as evidenced by narrower 95% CIs throughout the subgroups.
Determining the prevalence of psoriasis has substantial implications clinically, scientifically, and with regard to health policies. The adult prevalence rate of 3.0% continues to place psoriasis as one of the most common immune-mediated diseases affecting adults in the US. Because primary care clinicians will continue to be among the first to encounter people presenting with psoriasis, it is critical to educate them about the various clinical presentations of the disease, especially the presentation of psoriasis in people of color. Furthermore, because one-third of patients with psoriasis develop psoriatic arthritis, educational efforts should also focus on the screening, early recognition, and treatment of psoriatic arthritis and cardiometabolic, hepatic, and mental health comorbidities based on the joint American Academy of Dermatology and National Psoriasis Foundation guidelines.41
Several US and international organizations are key partners to researchers in the effort to characterize psoriasis prevalence. The National Psoriasis Foundation is a US-based, nonprofit patient advocacy organization committed to improving the lives of those living with psoriasis and psoriatic arthritis through advocacy, education, and research. The National Psoriasis Foundation has several ongoing initiatives that help further characterize the epidemiology of psoriasis.42 In addition, the Global Psoriasis Atlas is an international collaborative effort to provide information about the worldwide epidemiology of psoriasis.43 The Global Psoriasis Atlas also aims to evaluate access to treatment and comorbidity data from various countries.
Limitations
This study has some limitations. Based on the databases used to evaluate psoriasis prevalence, the precise estimates for psoriasis prevalence may differ due to differences in the study populations, methodology, and how psoriasis was classified in these databases.19,23,44 Several limitations exist with NHANES surveys. Because the NHANES questionnaire captures only those who had received a diagnosis of psoriasis from a health care professional, underestimation of psoriasis prevalence may have occurred by 0.4% to 2.28%.32 This underestimation occurs because, based on photographs of participants from the prior NHANES surveys, dermatologists identified psoriasis among participants who did not report carrying a physician-given diagnosis of psoriasis. Additionally, regarding self-reported psoriasis severity, the potential for overestimation of self-assessed body surface area may have occurred among those experiencing a substantial decrement in quality of life from psoriasis.
Conclusions
The results of this cross-sectional study suggest that the prevalence of psoriasis in the US population 20 years or older is 3.0% and that psoriasis remains one of the most common immune-mediated diseases affecting adults in the US. This prevalence has not differed significantly over the past decade. Based on the 2020 census data, psoriasis affects approximately 7.55 million US adults aged 20 years or older. These prevalence data are foundational to determining the burden of psoriasis and raising awareness of associated comorbidities. In addition, these data may help inform future epidemiologic research, clinician and patient education, and health policies to improve the lives of patients with psoriasis. To more accurately estimate psoriasis prevalence, future NHANES research efforts may consider an in-person dermatologist examination or total body photography to detect psoriasis in otherwise undiagnosed participants.
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