Background Alopecia areata (AA) is an autoimmune disorder characterized by patches of non-scarring alopecia affecting scalp and body hair that can be psychologically devastating. AA is clinically heterogenous, and its natural history is unpredictable. There is no preventative therapy or cure. Objective The objective of this study is to provide an evidence-based systematic review on the epidemiology and the burden of AA. Methods and selection criteria A search was conducted of the published, peer-reviewed literature via PubMed, Embase, and Web of Science. Studies published in English within the last 51 years that measured AA's incidence, prevalence, distribution, disability-adjusted life years (DALYs), quality of life, and associated psychiatric and medical comorbidities were included. Two authors assessed studies and extracted the data. Results The lifetime incidence of AA is approximately 2% worldwide. Both formal population studies found no sex predominance. First onset is most common in the third and fourth decades of life but may occur at any age. An earlier age of first onset corresponds with an increased lifetime risk of extensive disease. Global DALYs for AA were calculated at 1,332,800 in 2010. AA patients are at risk for depression and anxiety, atopy, vitiligo, thyroid disease, and other autoimmune conditions. Conclusion AA is the most prevalent autoimmune disorder and the second most prevalent hair loss disorder after androgenetic alopecia, and the lifetime risk in the global population is approximately 2%. AA is associated with psychiatric and medical comorbidities including depression, anxiety, and several autoimmune disorders, and an increased global burden of disease.

/pdf/epidemiology-and-burden-of-alopecia-areata-a-systematic-1k9ov82xgd.pdf

Epidemiology and burden of alopecia areata: a systematic review.

The skin provides both a physical barrier and an immunologic barrier to external threats. The protective machinery of the skin has evolved to provide situation-specific responses to eliminate pathogens and to provide protection against physical dangers. Dysregulation of this machinery can give rise to the initiation and propagation of inflammatory loops in the epithelial microenvironment that result in inflammatory skin diseases in susceptible people. A defective barrier and microbial dysbiosis drive an interleukin 4 (IL-4) loop that underlies atopic dermatitis, while in psoriasis, disordered keratinocyte signaling and predisposition to type 17 responses drive a pathogenic IL-17 loop. Here we discuss the pathogenesis of atopic dermatitis and psoriasis in terms of the epithelial immune microenvironment-the microbiota, keratinocytes and sensory nerves-and the resulting inflammatory loops.

The epithelial immune microenvironment (EIME) in atopic dermatitis and psoriasis.

Physicians are aware that climatic conditions negatively affect the skin. In particular, people living in equator far countries such as the Northern parts of Europe and North America are exposed to harsh weather during the winter and may experience dry and itchy skin, or deterioration of already existing dermatoses. We searched the literature for studies that evaluated the mechanisms behind this phenomenon. Commonly used meteorological terms such as absolute humidity, relative humidity and dew point are explained. Furthermore, we review the negative effect of low humidity, low temperatures and different seasons on the skin barrier and on the risk of dermatitis. We conclude that low humidity and low temperatures lead to a general decrease in skin barrier function and increased susceptible towards mechanical stress. Since pro-inflammatory cytokines and cortisol are released by keratinocytes, and the number of dermal mast cells increases, the skin also becomes more reactive towards skin irritants and allergens. Collectively, published data show that cold and dry weather increase the prevalence and risk of flares in patients with atopic dermatitis.

The effect of environmental humidity and temperature on skin barrier function and dermatitis

Objective 
To conduct a meta-analysis assessing the prevalence of vitiligo.
Methods 
Literatures that reported prevalence rates of vitiligo were identified using EMBASE, PubMed, the Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang database and Weipu database for the period from inception to May 2016. We performed stratified analyses on possible sources of bias, including areas difference, years of publication, gender and age. Publication bias was assessed with Egger’s test method.
Results 
A total of 103 studies were eligible for inclusion. The pooled prevalence of vitiligo from 82 population- or community-based studies was 0.2% (95%CI: 0.1%–0.2%) and from 22 hospital-based studies was 1.8% (95%CI: 1.4%–2.1%). A relatively high prevalence of vitiligo was found in Africa area and in female patients. For population- or community-based studies, the prevalence has maintained at a low level in recent 20 years and it has increased with age gradually. For hospital-based studies, the prevalence has showed a decreased trend from 60s till now or from young to old. No significant publication bias existed in hospital-based studies (t = 0.47, P = 0.643), while a significant publication bias existed in population- or community-based studies (t = 2.31, P = 0.026).
Conclusion 
A relatively high prevalence of vitiligo was found in Africa area and in female patients. The prevalence has maintained at a low level in recent years. It showed an inverse trend with age increment in population- or community-based studies and hospital-based studies.

/pdf/the-prevalence-of-vitiligo-a-meta-analysis-fe6mqigji3.pdf

The Prevalence of Vitiligo: A Meta-Analysis

Background Alopecia areata (AA) is a common autoimmune alopecia with heterogeneous severity and distribution. Previous studies found conflicting results about AA epidemiology. Objective To determine the prevalence, incidence, and predictors of AA, alopecia totalis, alopecia ophiasis, and alopecia universalis. Methods A systematic review of all published cohort and cross-sectional studies that analyzed AA and its subtypes. MEDLINE, Embase, LILACS, Scopus, Cochrane Library, and GREAT were searched. At least 2 reviewers performed study title/abstract review and data extraction. Random-effects meta-analysis was used because of significant heterogeneity (I2 = 99.97%). Results Ninety-four studies met the inclusion criteria. The pooled prevalence (95% confidence interval, N) of AA overall was 2.11% (1.82-2.42, N = 302,157,365), with differences of population-based (0.75% [0.49-1.06%], N = 301,173,403) and clinic-based (3.47% [3.01-3.96], N = 983,962) studies. The prevalences of alopecia totalis, ophiasis, and universalis were 0.08% (0.04-0.13, N = 1,088,149), 0.02% (0.00-0.06, N = 1,075,203), and 0.03% (0.01-0.06, N = 1,085,444), respectively. AA prevalence (95% confidence interval) increased over time ( 2009: 3.22% [2.59-3.92]; P  Conclusions AA affects 2% of the global population. AA prevalence is lower in adults than children, is increasing over time, and significantly differs by region.

Epidemiology of alopecia areata, ophiasis, totalis, and universalis: A systematic review and meta-analysis.

To clarify the prevalence of skin disorders among dermatology patients in Japan, a nationwide, cross-sectional, seasonal, multicenter study was conducted in 69 university hospitals, 45 district-based pivotal hospitals, and 56 private clinics (170 clinics in total). In each clinic, information was collected on the diagnosis, age, and gender of all outpatients and inpatients who visited the clinic on any one day of the second week in each of May, August, and November 2007 and February 2008. Among 67,448 cases, the top twenty skin disorders were, in descending order of incidence, miscellaneous eczema, atopic dermatitis, tinea pedis, urticaria/angioedema, tinea unguium, viral warts, psoriasis, contact dermatitis, acne, seborrheic dermatitis, hand eczema, miscellaneous benign skin tumors, alopecia areata, herpes zoster/postherpetic neuralgia, skin ulcers (nondiabetic), prurigo, epidermal cysts, vitiligo vulgaris, seborrheic keratosis, and drug eruption/toxicoderma. Atopic dermatitis, impetigo, molluscum, warts, acne, and miscellaneous eczema shared their top-ranking position in the pediatric population, whereas the most common disorders among the geriatric population were tinea pedis, tinea unguium, psoriasis, seborrheic dermatitis, and miscellaneous eczema. For some disorders, such as atopic dermatitis, contact dermatitis, urticaria/angioedema, prurigo, insect bites, and tinea pedis, the number of patients correlated with the average high and low monthly temperatures. Males showed a greater susceptibility to some diseases (psoriasis, erythroderma, diabetic dermatoses, inter alia), whereas females were more susceptible to others (erythema nodosum, collagen diseases, livedo reticularis/racemosa, hand eczema, inter alia). In conclusion, this hospital-based study highlights the present situation regarding dermatological patients in the early 21st century in Japan.

Prevalence of dermatological disorders in Japan: A nationwide, cross-sectional, seasonal, multicenter, hospital-based study

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Prevalence of dermatological disorders in Japan: A nationwide, cross-sectional, seasonal, multicenter, hospital-based study