Skin diseases: prevalence and predictors of itch and disease severity.

Chronic skin diseases are known to be common among the general population. Nevertheless, little research attention has been paid to patients with skin diseases in the general population, and consequently, little is known about the impact of skin diseases on daily life within this population. General definitions of health encompass different dimensions of disease outcome divided in disease severity, accompanying physical symptoms, and psychosocial well-being. These dimensions of disease outcome influence the impact of a disease on daily life. Additionally, it is generally assumed that disease outcome interacts with psychological factors. So far, research on disease outcome in patients with skin diseases has primarily focused on skin diseases most frequently encountered on dermatological wards, such as atopic dermatitis or psoriasis, leaving unaddressed many types of skin conditions and patients not seen on dermatological wards. Moreover, studies usually examine disease outcome at times when patients contact their health care provider, which is presumably when symptoms are worse, which might in turn lead to biased conclusions about the general impact of skin diseases on patients in daily life. Finally, few attempts have been made to investigate psychological factors associated with disease outcome in patients with skin diseases. Consequently, the role of specific psychological factors in the maintenance and exacerbation of skin diseases is unclear. The present thesis examines skin diseases both in general practice and on dermatological wards. First, the impact of skin diseases on general practice patients was investigated (chapter 2.1, 2.2 and 2.3) with emphasis on disease outcome according to general models of health. Then, this thesis evaluates the influence of psychological factors on disease outcome in patients with chronic skin diseases seen on dermatological wards. After a general review (chapter 3.1), this thesis particularly emphasizes on patients with psoriasis (chapter 3.2 and 3.3