Here we report the case of a 55-year-old Caucasian man with severe eosinophilic atopic asthma, who sequentially benefited from a treatment with mepolizumab, an anti-interleukin-5 monoclonal antibody, followed by treatment with dupilumab, an anti-interleukin-4/interleukin-13R antibody, the switch being justified by a flare-up of dermatitis while on mepolizumab. The gene discussed is IL5; the disease is skin disorder.