Asthma in patients with psoriasis

Funding sources: None. Conflicts of interest: None declared. Dear Editor, We read with interest the report by Fang et al.1 of the relationship between psoriasis and asthma in a large retrospective case–control study from Taiwan. The study found a 1·38‐fold increased risk of asthma among patients with psoriasis, with an increasing risk according to higher age of the patients. However, although adjustment for age, sex and selected comorbidities was performed, the study lacked important confounder control, particularly for smoking and body mass index. We studied the association between self‐reported asthma and psoriasis in a previously well‐described population of 34 781 Danish twins, aged 20–71 years, from the nationwide Danish Twin Registry.2 Psoriasis was identified by the question, ‘Has a doctor ever told you that you have, or have had psoriasis?’, whereas asthma was identified by the question, ‘Do you have, or have you ever had, asthma?’ The prevalences of psoriasis and asthma were 4·2% and 8·7%, respectively.