Background  Depression is a common mental health condition that has been associated with psoriasis. In the absence of prospective data, it remains unclear whether depression precedes psoriasis as a risk factor.

Objectives  To examine the association between depression and the risk of new-onset psoriasis.

Methods  A prospective cohort of 86 880 US female nurses, The Nurses’ Health Study II, was followed up from 1993 to 2005. Participants reported anti-depressant use and completed the Mental Health Index (MHI), a subscale of the Short-Form 36 in 1993. The MHI assessed for depression and scores was categorized into four strata: 0–52, 53–75, 76–85 and 86–100, with lower scores associated with increasing depressive symptoms. We excluded participants with a history of psoriasis prior to 1993. A self-report of incident physician-diagnosed psoriasis constituted the main outcome measure. For a sensitivity analysis, we had a subset of confirmed psoriasis cases.

Results  Depression was associated with an increased risk of incident psoriasis. Compared to women in the non-depressed group (MHI 86–100), women who reported either having high depressive symptomatology (MHI scores <52) or who were on anti-depressants had a multivariate relative risk (RR) of 1.59 for developing subsequent psoriasis (95% confidence interval [CI], 1.21–2.08). These associations became stronger among confirmed psoriasis cases.

Conclusions  We found that depression was independently associated with an increased risk of psoriasis in this population of US women.