Incident psoriasis in atopic dermatitis: A large-scale cohort study of disease- and treatment-associated risks

BackgroundClinical and genetic evidence on the association between atopic dermatitis (AD) and subsequent psoriasis remains conflicting, and it is unclear whether this risk is modified by systemic treatments. Recent reports suggest type 2-targeted biologics may unmask psoriasis in AD patients, but data are limited. We thus aimed to assess whether AD is associated with incident psoriasis and whether this risk differs by systemic treatment, particularly biologics versus conventional systemic immunosuppressants (cvIS). MethodsScoping analyses informed a locked analytic design, preregistration at OSF, and confirmatory execution. Propensity score-matched analyses compared AD with non-AD controls and biologics with cvIS. Sensitivity analyses, Cox model triangulation, and control outcomes assessed robustness. FindingsAmong [~]300,000 matched pairs, AD was associated with increased psoriasis risk (primary HR 3.81, 95% CI 3.35-4.34), consistent across all 8 sensitivity analyses and model triangulation. Biologic treatment was associated with reduced psoriasis risk versus cvIS (primary HR 0.20, 95% CI 0.11-0.35), consistent across 6 of 7 evaluable sensitivity analyses and Cox triangulation. Positive and negative control outcomes showed expected directional patterns. InterpretationAcknowledging limitations including residual confounding and coding misclassification, AD was associated with increased psoriasis risk and biologics with lower psoriasis risk than cvIS. FundingDFG (EXC2167, SFB1526, LU877/25-1), Schleswig-Holstein Excellence-Chair Program, Swedish Society for Dermatology and Venereology, and the Tore Nilson Foundation. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSAtopic dermatitis (eczema) and psoriasis are the two most common chronic inflammatory skin diseases worldwide. For a long time, doctors and researchers assumed these two conditions could not occur in the same person, as they were thought to involve opposing immune responses. However, this view has been challenged over the past decade. Some large studies, including population-based cohorts from Taiwan and the United Kingdom, have found that people with eczema may be at higher risk of developing psoriasis over time, while other studies, including genetic analyses, have suggested the opposite: that the two diseases may actually protect against each other. This conflicting picture has left clinicians uncertain about the true relationship between the two diseases in everyday clinical practice. A separate but related concern has emerged with the introduction of a new class of highly effective treatments for eczema, biologics, particularly dupilumab. Case reports and observational studies, including a large study published in JAMA Dermatology in 2025, have raised the possibility that these medications might trigger psoriasis in some patients, potentially by shifting the immune system from one inflammatory pattern to another. However, prior studies on this question had important methodological limitations: they were not pre-planned and registered before data collection, they did not always tightly link treatment use to an eczema diagnosis, and critically, none compared biologic treatment directly against conventional immunosuppressant medications, the most relevant clinical comparator. Added value of this studyThis study is a large and methodologically rigorous investigation of both questions: whether eczema itself increases the risk of developing psoriasis, and whether the type of systemic treatment used for eczema influences that risk. Using a database of over 110 million electronic health records from across the United States, we matched approximately 300,000 patients with eczema to 300,000 patients without eczema and followed them for up to seven years. We also compared nearly 5,500 patients treated with biologics to an equal number treated with conventional immunosuppressants. Crucially, our study was pre-registered before any data were analyzed, meaning the research questions, methods, and analyses were locked in advance and could not be adjusted based on what the data showed. We also used a range of additional analyses to test whether our findings were robust, including checks using outcomes that should not be affected by eczema or its treatment (such as appendectomy and hearing loss), which confirmed that our results were not likely explained by bias alone. We found that eczema was associated with an increased risk of developing psoriasis, but that this risk was substantially influenced by the choice of comparison group, ranging from approximately 1.4-fold to nearly 4-fold depending on the analytical approach. More strikingly, we found that patients treated with biologics had a markedly lower risk of developing psoriasis compared with those treated with conventional immunosuppressants, the opposite of what prior reports had suggested. This finding was consistent across nearly all additional analyses performed. Implications of all the available evidenceTaken together with existing evidence, these findings suggest two important conclusions. First, clinicians should be aware that eczema, particularly moderate-to-severe eczema requiring systemic treatment, may carry an elevated risk of developing psoriasis over time. This does not mean that all patients with eczema need to be screened for psoriasis routinely, but it does support clinical awareness and monitoring in higher-risk patients. Second, and perhaps most importantly for treatment decisions, biologics do not appear to increase the risk of psoriasis compared with conventional immunosuppressants and may in fact be associated with a lower risk. This provides reassurance for patients and clinicians considering biologic therapy and challenges the narrative that these medications trigger psoriasis. Future research should aim to confirm these findings in other populations, investigate the biological mechanisms underlying the relationship between eczema and psoriasis, and examine whether specific biologic agents differ from one another in their effects on psoriasis risk.