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Background: Psoriasis is a common skin disease and moderate to severe psoriasis is associated with a dose-dependent risk for metabolic and cardiovascular morbidity. It has previously been speculated that women have less severe psoriasis, as men are overrepresented in psoriasis registers and consume more care.

Objective: The objective of this study was to investigate, for the first time, the sex differences in the severity of psoriasis using the gold standard of severity measurement, the Psoriasis Area and Severity Index (PASI), and the distinct elements of the PASI score.

Design, Setting and Participants: This was a cross-sectional study based on the national registry for systemic treatment of psoriasis in Sweden (PsoReg), with 5438 patients experiencing moderate to severe psoriasis. Differences in the PASI score and its elements at enrolment were tested by multivariable ordinal logistic regressions.

Main Outcome Measures: The different components of the PASI score were used to analyze the assessment of disease severity. For each body area (head, arms, trunk, and legs), the score of the plaque characteristics and degree of skin involvement were used as outcomes.

Results: Women had statistically significantly lower median PASI scores (5.4) than men (7.3) [p < 0.001], which was consistent across all ages. The difference remained statistically significant in a multivariable linear regression. The itemized PASI analyses from the Mann–Whitney–Wilcoxon tests and the adjusted ordinal logistic regressions confirmed that women had significantly lower scores than men in all areas of the body, except for the head. No differences in the use of medications prior to enrolment could be found that may cause this difference between the sexes.

Conclusions: As the PsoReg contains the detailed disease measurement PASI, which was traditionally used for selected participants in clinical studies only, a nationwide unselected population could be investigated. The fact that women have less severe psoriasis can explain the dominance of males in the systemic treatment of psoriasis. These findings motivate a gender perspective in the management of psoriasis and in the prevention and management of its comorbidities.