Hypereosinophilic syndrome (HES) includes a spectrum of rare diseases that have increased blood eosinophils and tissue damage in common. The clinical manifestations are varied and may involve any organ system, but the heart, nervous system, bone marrow, and skin are commonly involved. HES is characterized by persistent and marked blood eosinophilia >1.5 × 109/L for more than 6 consecutive months with eosinophil-mediated organ damage or dysfunction, provided other potential causes for the damage have been excluded. The target organ damage mediated by eosinophils is highly variable in patients affected. Fifty percent of HES patients have cutaneous lesions as the first manifestation, which includes pruritic erythematous macules, papules, plaques, wheals, and nodules. Splinter hemorrhages and nail fold infarcts may herald the onset of thromboembolic disease. Eczematous lesions (involving hands, flexural areas, or dispersed plaques), erythroderma, and generalized thickening of the skin are also common. Urticaria and angioedema occur in all HES subtypes and are characteristic of lymphocytic HES variant.