The invention relates to a reflective optical element and an EUV lithography appliance containing one such element, said appliance displaying a low propensity to contamination. According to the invention, the reflective optical element has a protective layer system consisting of at least one layer. The optical characteristics of the protective layer system are between those of a spacer and an absorber or correspond to those of a spacer. The selection of a material with the smallest possible imaginary part and a real part which is as close to 1 as possible in terms of the refractive index leads to a plateau-type reflectivity course according to the thickness of the protective layer system between two thicknesses d1 and d2. The thickness of the protective layer system is selected in such a way that it is less than d2.