According to the National Institutes of Health (NIH), approximately 2.2% of the United States population has psoriasis. Internationally, the incidence of psoriasis varies dramatically. A study of 26,000 South American Indians did not reveal a single case of psoriasis, whereas in the Faeroe Islands, an incidence of 2.8% was observed. Overall, approximately 2-3% of people are affected by psoriasis worldwide. Psoriasis can begin at any age, yet there is a bimodal peak between age 20-30 years and 50-60 years. Approximately 10-15% of new cases begin in children younger than 10 years. The median age at onset is 28 years.
Psoriasis appears to be slightly more prevalent among women than among men; however, men are thought to be more likely to experience the ocular disease. Psoriasis is slightly more common in women than in men.
The incidence of psoriasis is dependent on the climate and genetic heritage of the population. It is less common in the tropics and in dark-skinned persons. Psoriasis prevalence in African Americans is 1.3% compared with 2.5% in whites. 
Psoriasis, even severe psoriasis, may occur in the pediatric age group, with a prevalence of 0.5-2% of children. Both biologic and immunomodulating therapies may be used safely and effectively. 
Although psoriasis is usually benign, it is a lifelong illness with remissions and exacerbations and is sometimes refractory to treatment. It progresses to arthritis in about 10% of cases. About 17-55% of patients experience remissions of varying lengths.
Mild psoriasis does not appear to increase risk of death.  However, men with severe psoriasis died 3.5 years earlier compared with men without the disease. Women with severe psoriasis died 4.4 years earlier compared with women without the disease. 
Psoriasis is associated with smoking, alcohol, metabolic syndrome, lymphoma, depression, suicide, potentially harmful drug and light therapies, and possibly melanoma and nonmelanoma skin cancers.
In a population-based cross-sectional study of 9035 psoriasis patients and 90,350 matched controls without psoriasis, those with more extensive psoriatic skin disease were at greater risk for major medical comorbidities, including heart and blood vessel disease, chronic lung disease, diabetes, kidney disease, joint problems, and other health conditions. [17, 18] Overall, the risk for any other type of serious illness was 11% higher for people with mild psoriasis, 15% higher for patients with moderate psoriasis, and 35% higher for those with severe psoriasis. [17, 18]
A systematic review of 90 studies confirmed that patients with psoriasis had a higher risk of ischemic heart disease, stroke, and peripheral arterial disease but also a greater prevalence of risk factors for cardiovascular disease, compared with controls. The authors concluded that large prospective studies with long-term followup are required to determine whether psoriasis is an independent risk factor for vascular disease or is merely associated with known risk factors.  Another study identified psoriasis as an independent risk factor for cardiovascular disease in women, especially if they had psoriatic arthritis and suffered from psoriasis for a longer time period (>9 y). 
In a population-based cross-sectional study of 1322 hypertensive patients with psoriasis and 11,977 controls without psoriasis, Takeshita et al found that patients with psoriasis were more likely to suffer from uncontrolled hypertension than those without psoriasis. [21, 22] Patients with moderate-to-severe psoriasis affecting more than 3% of their body surface area were at the greatest risk.
The dose-response relation between uncontrolled hypertension and psoriasis severity remained significant after adjustment for age, sex, body mass index, smoking status, alcohol use, comorbid conditions, and current use of antihypertensive medications and nonsteroidal anti-inflammatory drugs, with odds ratios of 1.20 (95% confidence interval [CI], 0.99-1.45) for moderate psoriasis and 1.48 (95% CI, 1.08-2.04) for severe psoriasis. 
Severe psoriasis was associated with a greatly increased risk of chronic kidney disease (CKD) in a recent study of more than 800,000 patients, including 142,883 with psoriasis, 7354 with severe psoriasis, and 689,702 without psoriasis. After adjustment for age, sex, cardiovascular disease, diabetes mellitus, hyperlipidemia, hypertension, use of nonsteroidal anti-inflammatory drugs, and body mass index, the adjusted hazard ratio for CKD among patients with severe psoriasis was 1.93. [23, 24]
In a nested analysis of 8731 psoriasis patients and 87,310 controls, the odds ratio of CKD after adjustment for age, sex, cardiovascular disease, diabetes, hypertension, hyperlipidemia, body mass index, use of nonsteroidal anti-inflammatory drugs, and duration of observation was 1.36 in patients with moderate psoriasis and 1.58 in those with severe psoriasis. The relative risk for CKD was highest in younger patients. [23, 24]
Psoriasis can significantly influence a person’s quality of life. The physical and mental disability experienced with this disease can be comparable or in excess of that found in patients with other chronic illnesses such as cancer, arthritis, hypertension, heart disease, diabetes, and depression. A study by Kurd et al further supports the notion that psoriasis impacts quality of life and potentially long-term survival.  There should be a higher clinical suspicion for depression in the patient with psoriasis.
While the clinical presentation of psoriasis, and whatever improvements are made during therapy, is usually measured using the PASI (Psoriasis Area and Severity Index) score, measurement of the effect on the quality of life of the psoriasis patient may be better assessed by the DLQI (Dermatology Life Quality Index) or the CDLQI (Children’s Dermatology Life Quality Index). Measurements using these tools generally show improved quality of life with more aggressive treatment such as systemic agents. [26, 27]
Studies show that psoriasis of the palms and soles tend to have greater impact on the patient’s quality of life compared to those with more extensive psoriatic involvement not involving the palms and soles. [28, 29]
Dry eye and its manifestations may be present. Avoiding drying conditions and using lubricants can be effective. Patient recognition of these symptoms is vital for effective early treatment of this disease. Most cases of psoriasis can be controlled at a tolerable level with the regular application of care measures.
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