Alternative models of comorbidity: a framework for the interpretation of epidemiological association studies.

Relationships between chronic diseases have emerged as major clinical, public health and research issues. Consequently, clinical and epidemiological research on comorbidities of skin diseases is increasingly recognized as an important tool to understand their etiologies more fully and to capture their morbidities and burdens. In this issue, Flohr and colleagues report a cross-sectional analysis on the complex associations among atopic dermatitis, filaggrin loss-of-function mutations, skin barrier function, and food sensitization in exclusively breastfed infants. When interpreting this and other association studies, various alternative models of comorbidity should be considered as suggested by Neale and Kendler.