Comorbidities in Atopic Dermatitis: An Update and Review of Controversies.

Early onset of atopic dermatitis is considered a risk factor for any atopic disease, especially when the skin manifestations are persistent, and there is sensitization to multiple allergens and a family history. Atopic dermatitis is also thought to exert a synergistic effect with inflammation present in other organs and systems, as is the case in other immune-mediated inflammatory diseases. Most studies show a statistical relationship between obesity, various cardiometabolic comorbid conditions, and atopic dermatitis; this relationship is more marked when the disease is more severe or active over a longer period of time. However, other than epidemiological assessments, few studies provide in-depth evidence of functional mechanisms. Furthermore, various confounders, such as deterioration of quality of life and the psychological aspects of atopic dermatitis, could favor unhealthy habits, including a sedentary lifestyle and smoking, which could in turn increase the risk of morbidity and mortality. Chronic inflammation with differentiation toward a type 2 helper T cell pattern and the long-term use of immunosuppressants could be risk factors for some hematologic diseases, although they could exert a protective effect in others. The presence of proinflammatory cytokines capable of crossing the blood-brain barrier could favor an increase in the frequency of psychological diseases (eg, depression, anxiety, and suicidal ideation) and attention disorders (eg, attention deficit or hyperactivity). However, other factors, such as chronic pruritus and sleep disorders, could also play roles.